El Centro Fellows
The El Centro Fellows have expertise in and commitment to Latin America, support SWJ's particular focus on the small wars in the region, and agree with SWJ's general approach to advancing discussion and awareness in the field through community dialog and publishing.
El Centro Associates are actively engaged in research or practice in the region and in transnational organized crime or insurgency. The Fellows have already made significant and distinguished contributions to the field through the course of their career. The Senior Fellows are Fellows that are central to producing SWJ El Centro and are very active in managing our work in this focus area.
- Robert J. Bunker
- John P. Sullivan
- José de Arimatéia da Cruz
- Luis Astorga
- Michael L. Burgoyne
- Edgardo Buscaglia
- Irina A. Chindea
- Steven S. Dudley
- Douglas Farah
- Vanda Felbab-Brown
- Luis Jorge Garay-Salamanca
- Ioan Grillo
- Gary J. Hale
- Nathan Jones
- Paul Rexton Kan
- Robert Killebrew
- Max G. Manwaring
- Molly Molloy
- Robert Muggah
- Luz E. Nagle
- Eduardo Salcedo-Albarán
- Robert H. Scales
- Pamela Ligouri Bunker
- Marisa Mendoza
- Angelo Thomas
- George W. Grayson
- Graham H. Turbiville, Jr.
In alphabetical order, by last name:
José de Arimatéia da Cruz is a Visiting Research Professor, U.S. Army War College, Carlisle Barracks, Carlisle, PA. He is also a Professor of International Relations and Comparative Politics, Department of Criminal Justice, Social & Political Science, Armstrong Atlantic State University, Savannah, Georgia. He holds a Ph.D. in Political Science, Miami University, Oxford, Ohio; M.A. in Political Science/Political Philosophy, Miami University, Oxford, Ohio; M.S. in Criminal Justice (Cyber Affairs and Security) Armstrong Atlantic State University, Savannah, Georgia; and B.A. in Philosophy, Wright State University, Dayton, Ohio. He has published in the Journal of Politics & Policy, Studies Revue Canadienne des Etudes Latino-Americaines et Caraib, Law Enforcement Executive Forum, International Social Science Review, The Latin Americanist, Latin American Politics and Society, and Journal of Third World Studies.
Luis Astorga holds a PhD in Sociology from the University of Paris 1. He is a researcher at the Institute of Social Research of the National Autonomous University of Mexico (UNAM–Universidad Nacional Autónoma de México); coordinator of the UNESCO Chair “Economic and social transformations connected with the international drug problem;” member of the National System of Researchers (SNI) and the Mexican Academy of Sciences (AMC); Author of: Seguridad, traficantes y militares (Security, drug traffickers and the military), México, Tusquets, 2007; Drogas sin fronteras (Drugs without borders), México, Grijalbo, 2003; El siglo de las drogas (The drugs century), México, Plaza y Janés, 2005 (Espasa-Calpe, 1996); and Mitología del ‘narcotraficante’ en México (Drug trafficker’s mythology in Mexico), México, UNAM/Plaza y Valdés, 1995. He has also published chapters in books, and articles about drug trafficking in México in scientific journals from Mexico, The United States of America, Colombia, France, Italy, India, Great Britain and Belgium.
Michael L. Burgoyne is a Lieutenant Colonel and a US Army Foreign Area Officer, has served in various policy and security cooperation positions in the Americas including assignments as the Army Attaché in Mexico City and the Andean Ridge Desk Officer at U.S. Army South. As a policy analyst in the Office of National Drug Control Policy in the Executive Office of the President, he focused on counterdrug coordination with Mexico and the development of national efforts against transnational organized crime. LTC Burgoyne deployed twice in support of Operation Iraqi Freedom in command and staff positions. He is the co-author of The Defense of Jisr al-Doreaa, a tactical primer on counterinsurgency. LTC Burgoyne is an adjunct instructor at the University of Arizona’s International Security Studies program where he teaches Mexican National Security and Transnational Organized Crime and National Security. He holds a B.A. from the University of Arizona and an M.A. in Security Studies from Georgetown University.
Pamela Ligouri Bunker is a researcher and analyst specializing in international security and terrorism and is a past senior officer of the Counter-OPFOR Corporation. She holds undergraduate degrees in anthropology-geography and social sciences from California State Polytechnic University Pomona, an M.A. in public policy from the Claremont Graduate University, and an M.Litt. in terrorism studies from the University of Saint Andrews, Scotland. She is co-editor of Global Criminal and Sovereign Free Economies and the Demise of the Western Democracies: Dark Renaissance (Routledge, 2015) and has published many other referred and professional works.
Robert J. Bunker is an Adjunct Research Professor, Strategic Studies Institute, US Army War College and Adjunct Faculty, Division of Politics and Economics, Claremont Graduate University. He holds university degrees in political science, government, social science, anthropology-geography, behavioral science, and history and has undertaken hundreds of hours of counterterrorism training. Past professional associations include Distinguished Visiting Professor and Minerva Chair at the Strategic Studies Institute, U.S. Army War College; Futurist in Residence, Training and Development Division, Behavioral Science Unit, Federal Bureau of Investigation Academy, Quantico, VA; Staff Member (Consultant), Counter-OPFOR Program, National Law Enforcement and Corrections Technology Center-West; and Adjunct Faculty, National Security Studies M.A. Program and Political Science Department, California State University, San Bernardino, CA. Dr. Bunker has hundreds of publications including Studies in Gangs and Cartels, with John Sullivan (Routledge, 2013), Red Teams and Counterterrorism Training, with Stephen Sloan (University of Oklahoma, 2011), and edited works, including Global Criminal and Sovereign Free Economies and the Demise of the Western Democracies: Dark Renaissance (Routledge, 2014), co-edited with Pamela Ligouri Bunker; Criminal Insurgencies in Mexico and the Americas: The Gangs and Cartels Wage War (Routledge, 2012); Narcos Over the Border: Gangs, Cartels and Mercenaries (Routledge, 2011); Criminal-States and Criminal-Soldiers (Routledge, 2008); Networks, Terrorism and Global Insurgency (Routledge, 2005); and Non-State Threats and Future Wars (Routledge, 2002).
Edgardo Buscaglia is a Senior Scholar in Law and Economics at Columbia University; the Director of the International Law and Economics Development Centre; and the President of the Institute for Citizens Action in Mexico. Professor Dr. Buscaglia currently serves as Visiting Professor at the Universidad de San Andrés (Argentina) and has served as Visiting Professor of Law and Economics at the Mexican Autonomous Institute of Technology (ITAM–Instituto Tecnológico Autónomo de México–ITAM) between 2003-2011 and at the National Autonomous University of Mexico (UNAM–Universidad Nacional Autónoma de México) in 2013, Georgetown University 1995-1996 and Hamburg University (Germany) in 2014. Prof. Dr. Buscaglia was affiliated as a Fellow with the Hoover Institution, Stanford University, and Director of the International Law and Economic Development Center at the University of Virginia. He also served as UN staff and external adviser to the United in Afghanistan and with The World Bank. In 1995, he co-founded the Latin-American and Caribbean Law and Economics Association (ALACDE). He received his legal postdoctoral training in the Jurisprudence and Social Policy Program at the University of California at Berkeley and received a master’s in law and economics and a PhD in Economics from the University of Illinois at Urbana-Champaign in 1989.
Irina A. Chindea is an Associate Political Scientist with the Washington D.C. office of the RAND Corporation. Irina's research interests focus on transnational illicit networks, irregular warfare, asymmetric threats, the nexus between finance and the activities of non-state armed groups, with a regional focus on Latin America and the Middle East. Irina has conducted extensive field research in Mexico, Colombia, El Salvador, and Canada for her doctoral dissertation on patterns of cooperation and conflict among criminal organizations. She holds a Ph.D. in International Relations and an M.A. in Law and Diplomacy from The Fletcher School at Tufts University, and a B.Sc. in Business Administration from the Academy of Economics in Bucharest, Romania. Prior to joining RAND, she was a post-doctoral research fellow in the International Security Program at the Belfer Center at Harvard’s Kennedy School, and a Visiting Assistant Professor with University at Albany (SUNY), where she taught classes on International Relations Theory, Comparative Foreign Policies, Homeland Security, and Research Methods.
Steven S. Dudley is the co-director of InSight, a new non-profit initiative with offices in Bogotá and Washington DC that monitors organized crime in the Americas. He is the former Bureau Chief of The Miami Herald in the Andean Region and the author of Walking Ghosts: Murder and Guerrilla Politics in Colombia (Routledge, 2004). Dudley has also reported from Mexico, Haiti, Brazil, Nicaragua, Cuba, and Miami for National Public Radio, the BBC, and The Washington Post, among others. In addition to his work at InSight, he has done a documentary film on the life and career of a lawyer that defends Colombian drug traffickers and paramilitaries, and he has written policy briefs for the Woodrow Wilson Center for International Scholars and the International Crisis Group. Dudley has a B.A. in Latin American History from Cornell University and an M.A. in Latin American Studies from the University of Texas at Austin. He has won numerous journalism prizes and was awarded the prestigious Knight Fellowship at Stanford University in 2007.
Douglas Farah is president of IBI Consultants, LLC and senior visiting fellow at the Center for Complex Operations at National Defense University. He specializes in field research, works as a consultant and subject matter expert on security challenges, terrorism and transnational organized crime in Latin America, both for the U.S. government and the private sector. For the two decades before consulting (1985-2005), Farah worked as a foreign correspondent and investigative reporter for The Washington Post covering the civil wars in Central America and the drug wars in the Andean region. He is the author of dozens of articles and monographs in peer reviewed journals and the media and Blood From Stones: The Secret Financial Network of Terror (2004) and Merchant of Death: Money, Guns, Planes and the Man Who Makes War Possible (with Stephen Braun, 2007).
Vanda Felbab-Brown is a fellow in Foreign Policy at the Brookings Institution, in the 21st Century Defense Initiative and the Latin America Initiative. She is an expert on illicit economies and international and internal conflicts and their management, including counterinsurgency. She focuses particularly on South Asia, Burma, the Andean region, Mexico, and Somalia. Dr. Felbab-Brown is the author of Shooting Up: Counterinsurgency and the War on Drugs (Brookings Institution Press, 2009) which examines military conflict and illegal economies in Colombia, Peru, Afghanistan, Burma, Northern Ireland, India, and Turkey. She is also the author of numerous policy reports, academic articles, and opeds. A frequent commentator in U.S. and international media, Dr. Felbab-Brown regularly testifies on these issues in the U.S. Congress. She received her Ph.D. in political science from MIT and her B.A. from Harvard University.
Luis Jorge Garay-Salamanca is an industrial engineer and Magister in Economics at the Universidad de los Andes (Bogotá, Colombia), and PhD in Economics at the Massachusetts Institute of Technology. He is the Academic Director at the Vortex Foundation. Dr. Garay has been a Visiting Scholar at the Universities of Oxford and Cambridge. He teaches at the Universities de los Andes and Nacional de Colombia. He served as a Visiting Scholar and Consultant at the InterAmerican Development Bank, and as a Consultant at the United Nations Program for Development in Colombia, the National Planning Department and Ministries of Finance, Foreign Trade and Foreign Affairs in Colombia. At the present is the director of the National Process of Verification of Human, Social and Economic Rights of the forced displaced population in Colombia. He has authored more than 40 books and published numerous essays in specialized journals in Colombia and the United States, in topics like international migration and remittances, international trade and economic integration, foreign debt management, industrial development and international competitiveness, globalization, corruption and capture of State, and social exclusion.
George W. Grayson was a founding El Centro fellow until his death in 2015. He was 1938 Professor of Government Emeritus at the College of William and Mary. He was a specialist on Latin American Politics, with a particular interest in Mexico. He wrote over 30 books and monographs on international affairs. Most recently, these include The Cartels: The Story of Mexico's Most Dangerous Criminal Organizations and Their Impact on U.S. Security (Prager, 2013) and The Executioner’s Men: Inside Los Zetas (co-authored with Sam Logan, Transaction Press, 2012). His other publications include: Consequences of Vigilantism in Mexico for the United States (Strategic Studies Institute, U.S. Army War College, 2011); Mexico: Narco-Violence and a Failed State? (Transaction, 2010), La Familia Drug Cartel: Implications for U.S.-Mexican Security (Strategic Studies Institute, U.S. Army War College, 2010); Mexico’s Struggle with Drugs and Thugs (Foreign Policy Association, 2009); and Mexican Messiah: Andres Manuel Lopez Obrador (Penn State University Press, 2007). He served as a member of the Virginia House of Delegates for 27 years and was a Senior Associate at the Center for Strategic & International Studies in Washington, D.C. and an Associate Scholar of the Foreign Policy Research Institute in Philadelphia. Grayson earned his B.A. at the University of North Carolina (Chapel Hill), his M.A. and Ph.D. at the Johns Hopkins University (Nitze School of Advanced International Studies), and a J.D. at the William and Mary's Marshall-Wythe School of Law. He was a member of Phi Beta Kappa.
Ioan Grillo is a journalist and writer based in Mexico City. He has covered Latin America since 2001 for media including Time Magazine, the New York Times, Reuters, BBC, Letras Libres and many others. He specializes on drugs cartels, gangs and crime wars. He has also worked on documentaries for the History Channel, National Geographic, and Al Jazeera. He is the author of Gangster Warlords: Drug Dollars, Killing Fields and the New Politics of Latin America (2016) and El Narco: Inside Mexico’s Criminal Insurgency (2011).
Gary J. Hale is a law enforcement and intelligence professional who retired from the federal government in 2010 after a 37-year career with various intelligence community and federal law enforcement agencies. His last assignment was as the Chief of Intelligence in the Houston Field Division of the Drug Enforcement Administration (DEA). Hale also served with the Army Security Agency from 1972-1978 throughout Europe. He joined the DEA in 1979 while serving as a Task Force Agent and Narcotics Officer detached from the Laredo, Texas Police Department where he served from 1978-1979. While at DEA he served at the El Paso Intelligence Center (EPIC), La Paz, Bolivia, Bogotá, Colombia, New Orleans, Boston, and Washington, D.C. Hale was also assigned as the DEA intelligence chief at the U.S. Embassy in Mexico City where he participated in the hunt for Amado Carrillo-Fuentes, the “Lord of the Skies.” In 2011 and 2012, he served as the Law Enforcement-Intelligence Program Coordinator for the Merida Initiative at the U.S. Embassy in Mexico City. Hale has a Bachelor of Science in Computer Science (Franklin Pierce University), a Master’s Degree in Judicial Policy (Universidad de Almería, España), and is an alumnus of the Harvard University Kennedy School of Government and the University of Virginia’s Darden School of Leadership. In 2010, Hale was appointed as a Drug Policy Fellow at the James A. Baker III Institute for Public Policy at Rice University in Houston, Texas.
Nathan Jones is an Assistant Professor of Security Studies at Sam Houston State University and a Non-resident Scholar for Rice University’s Baker Institute Mexico Center. He holds a PhD from the University of California, Irvine and won an Institute for Global Conflict and Cooperation Fellowship to conduct fieldwork in Mexico on organized crime. He participated in the National Defense Intelligence College-University of San Diego Mexico Project. He presented his work “The Four Phases of the Arellano Felix Organization” at the University of Guadalajara, the University of San Diego and the National Defense Intelligence College in Washington, D.C. He also served as an adjunct instructor at the University of San Diego, Trans-Border Institute. Jones recently published Mexico's Illicit Drug Networks and the State Reaction (Georgetown University Press, 2016).
Paul Rexton Kan is currently Professor of National Security Studies at the US Army War College. He is also the author of the books Drugs and Contemporary Warfare (Potomac Books, 2009) and Cartels at War: Mexico's Drug Fueled Violence and the Threat to US National Security (Potomac Books, 2012). His most recent book is Drug Trafficking and International Security (Rowman and Littlefield, 2016). In 2011, he was the Senior Visiting Counternarcotics Advisor with ISAF in Kabul, Afghanistan.
Robert Killebrew is a private consultant in national defense issues. He is a retired Army infantry colonel with service in U.S. Army Special Forces and airborne units, and he has taught national and military strategy at the Army War College. He is a Non-Resident Senior Fellow with the Center for a New American Security and co-author of Crime Wars; Gangs, Cartels and U.S. National Security (CNAS, 2010).
Max G. Manwaring, is a retired Professor of Military Strategy at the Strategic Studies Institute of the US Army War College, has held the General Douglas MacArthur Chair of Research at the USAWC, and is a retired US Army colonel. Over the past 30+ years, he has served in various military and civilian positions. They include the US Southern Command, the Defense Intelligence Agency, Dickinson College, and Memphis University. Dr. Manwaring is the author and co-author of several articles, chapters, and books dealing with intra-national and international security affairs, political-military affairs, insurgency, counter-insurgency, and gangs. His most recent book The Complexity of Modern Irregular War, was published by the University of Oklahoma Press, 2012. His most recent article is “El lexico de seguridad desde Wesfalia hasta hoy: Un cuento aleccionador” (“The Security Lexicon from Westphalia to Today: A Cautionary Tale”), was published in the Air and Space Power Journal in Español, 2017. Manwaring’s forthcoming book, Confronting the Evolving Global Security Landscape: Lessons from the Past and Present, Praeger, is scheduled for publication in April 2019. Dr. Manwaring is a graduate of the U.S. Army War College, and holds an M.A. and a Ph.D. in political science from the University of Illinois. Dr. Manwaring remains active in the national security community, and may be contacted at email@example.com.
Marisa Mendoza is a PhD student in Political Science, with a concentration in Policy, at Claremont Graduate University. She has extensive expertise in developing government contracts and large-scale grant proposals to fund academic, support services, and re-entry programs for high-risk, underserved populations. Ms. Mendoza holds an Executive MBA from the Drucker School of Management, Claremont Graduate University and a Masters of Social Work (MSW) and BS in General Studies (English concentration) from the University of Southern California. She is currently completing her doctoral dissertation on the transnational street gang Mara Salvatrucha (MS-13) and the various domestic/international policies that have influenced its forty-year evolution. She is fluent in Spanish and focuses on open source research methods, including translation of social media postings, government documents, and various forms of media coverage.
Molly Molloy is a research librarian and border and Latin American specialist at the New Mexico State University Library in Las Cruces, NM. She is the creator and editor of the Frontera List, a forum for news and discussion of border issues. Since 2008 she has provided detailed documentation of homicides in Mexico, with an emphasis on Ciudad Juarez. More than 11,000 people have been murdered in Juarez since 2008, making that border city the epicenter of the recent hyperviolence in Mexico. She translated and co-edited El Sicario: The Autobiography of a Mexican Assassin (Nation Books, 2011) and has written for The Nation, Phoenix New Times [here and here], Narco News Bulletin, and other publications. Molloy is often called upon to consult with academic researchers, attorneys and journalists about the violence in Mexico.
Robert Muggah co-founded the Igarapé Institute, a think and do tank working at the interface of security and development. He is also executive director of the SecDev Group, a digital risk group. He is a non-resident fellow or faculty at Singularity University, the Graduate Institute in Geneva, the University of British Columbia and the University of San Diego. Before that he directed research at the Small Arms Survey (2000-2011). Robert works with the Inter-American Development Bank, McKinsey´s, the United Nations and World Bank, among others, in over 30 countries. He is a regular contributor to the Guardian, Globe and Mail, Los Angeles Times, New York Times and other media outlets. He delivered talks at TED in 2017 and 2015, the Web Summit, and the World Economic Forum (WEF) in Davos, Dubai, Medellin and Geneva. He is the founder and executive editor of Stability Journal and serves on the editorial board of several academic journals. Robert is also affiliated with the WEF Council on Cities and Urbanization, the 2018 and 2019 Global Risk Report, the Global Initiative Against Transnational Organized Crime, the Know Violence in Childhood Initiative, the Chicago Council on Global Affairs, the Canadian Global Affairs Institute, and other international networks. He earned his PhD from the University of Oxford. He can be contacted at firstname.lastname@example.org.
Luz E. Nagle is a former Colombian judge and a Professor of Law at Stetson University College of Law, specializing in international law and international criminal law. She serves as an External Researcher in the Strategic Studies Institute of the US Army War College, and has been involved as a trainer and advisor in several rule of law and military reform projects sponsored by the U.S. Departments of Defense, Justice, and State in Argentina, Colombia, Mexico, and Panama. She is active in several international legal societies and currently holds seats on the ABA’s Criminal Justice Council and on the International Bar Association’s Legal Practice Division Council. Her scholarship focuses on US foreign policy and regional security in the Americas, internal armed conflict, and transborder crime.
Eduardo Salcedo-Albarán is the current Director of SciVortex. By applying artificial intelligence, neuroscience and social networks analysis, he has researched in the areas of transnational organized crime, kidnapping, corruption, drug-trafficking and State Capture. He served as advisor for the Colombian Presidency and security agencies in Colombia. He has also worked with foundations, institutes, and public and private agencies in Latin America and the United States. He is part of EDGE Foundation, composed by thinkers “who are at the center of today's intellectual, technological, and scientific landscape”. Some of his books: Corrupción, Cerebro y Sentimientos (2007), La Mente Inorgánica (2009), El Crimen Como Oficio (2007), La Captura y Reconfiguración Cooptada del Estado (2009), and Illicit Networks Reconfiguring States: Social Network Analysis of Colombian and Mexican Cases (2010).
Robert H. Scales is one of America’s best known and most respected authorities on land warfare. He is currently President of Colgen, Inc, a consulting firm specializing in issues relating to landpower, wargaming and strategic leadership. Prior to joining the private sector Dr. Scales served over thirty years in the Army, retiring as a Major General. He commanded two units in Vietnam, winning the Silver Star for action during the battles around Dong Ap Bia (Hamburger Hill) during the summer of 1969. Subsequently, he served in command and staff positions in the United States, Germany, and Korea and ended his military career as Commandant of the United States Army War College. He is the author of Certain Victory, Firepower in Limited War, Future Warfare, Yellow Smoke: the Future of Land Warfare for America’s Military, The Iraq War: a Military History (with Williamson Murray), and Texas Border Security: A Strategic Military Assessment (with Barry McCaffrey). He is a graduate of West Point and earned his PhD in history from Duke University.
John P. Sullivan was a career police officer. He retired as a lieutenant with the Los Angeles County Sheriff’s Department. He is also an adjunct researcher at the Vortex Foundation in Bogotá, Colombia; a member of the Scientific Advisory Committee of the Global Observatory of Transnational Criminal Networks; a senior research fellow at the Center for Advanced Studies on Terrorism (CAST); a Global Fellow at Stratfor (2018); and an instructor at the Safe Communities Institute at the Sol Price School of Public Policy at the University of Southern California. He is co-editor of Countering Terrorism and WMD: Creating a Global Counter-Terrorism Network (Routledge, 2006) and Global Biosecurity: Threats and Responses (Routledge, 2010) and co-author of Mexico’s Criminal Insurgency: A Small Wars Journal-El Centro Anthology (iUniverse, 2011) Studies in Gangs and Cartels (Routledge, 2013). Most recently he co-edited Blood and Concrete: 21st Century Conflict in Urban Centers and Megacities (Xlibris, 2019) and The Rise of The Narcostate (Mafia States) (Xlibris, 2018). He completed the CREATE Executive Program in Counter-Terrorism at the University of Southern California and holds a Bachelor of Arts in Government from the College of William and Mary, a Master of Arts in Urban Affairs and Policy Analysis from the New School for Social Research, and a PhD from the Open University of Catalonia (Universitat Oberta de Catalunya) in Barcelona. His doctoral thesis was “Mexico’s Drug War: Cartels, Gangs, Sovereignty and the Network State.” His current research focus is the impact of transnational organized crime on sovereignty in Mexico and other countries.
Angelo Thomas is in the International Baccalaureate program at Claremont High School. He is President of the Model United Nations club, and a Reagan Great Communicator Debate national Qualifier. He is a captain of the Speech and Debate team, and has placed in the top 8 at the National Debate Tournament. Past travels include England, France, and Italy. His El Centro research focus is on third generation gangs with an emphasis on 18th Street (Barrio 18) activities in the United States and Central America.
Graham H. Turbiville, Jr. was involved as a founding El Centro fellow until his death in April, 2012. He was a Senior Consultant and Researcher for Courage Service, Inc., McLean, Virginia (a Centra Technology Company), addressing Department of Defense and Intelligence Community programs dealing with cultural and geographic assessments in several areas of the world; a Senior Consultant for the Tribal Analysis Center, Leesburg, Virgina, producing history-based assessments of tribal/clan societies in contemporary war and conflict; and an Associate Fellow with the US Special Operations Command/ Joint Special Operations University (USSOCOM/JSOU). Earlier, Dr. Turbiville served 30 years in intelligence community analytical and leadership positions at the Defense Intelligence Agency and the Department of the Army. These included as director/chief of long-range and current intelligence offices and directorates, director of a Joint Reserve Intelligence Center, and other assignments dealing with foreign combined arms, security, and special operations forces.