The use of drones, or unmanned aerial vehicles, by the US to attack alleged terrorists overseas started during the George W. Bush administration and accelerated during the Obama administration. According to reports, the US has carried out over 14,000 such attacks in Afghanistan, Pakistan, Somalia, and Yemen since 2004. Drone operations that assassinate Islamic terrorists may result in more terrorist acts, not less. They also result in a startling number of civilian casualties: some studies estimate that a third of drone deaths are civilians, while others estimate that the number is even higher.