The conduct of war in the modern era has been a complicated matter. But in the 21st century, at a time when the United States is engaged in the longest war in its history, unprecedented changes have been introduced that involve major increases in that complexity. A new regimen of legal and judicial restrictions has been imposed on the military forces that are engaged in combat operations necessary for the national defense. This has raised a host of questions and practical problems that affect all three branches of the federal government.