Amid a growing debate over how to bring down the government’s debt, a new study has concluded that U.S. involvement in Afghanistan, Iraq and Pakistan has cost up to $4 trillion over the past decade. The study, by the nonpartisan Eisenhower Research Project based at Brown University’s Watson Institute for International Studies, also estimates that at least 225,000 people, including civilians, troops and insurgents, have died as a result of the conflicts.