The Constitution of the United State gives Congress the express power to declare war, so any formal declaration of war must be by joint resolution of that body. However, declarations of war are somewhat outdated. The last formal declaration of war issued by the U.S. was against Japan in World War II. Since that time, American troops have been committed to combat numerous times by virtue of the President's position as Commander in Chief of the Armed Forces. Additionally, the United Nations charter prohibits the use or threat of force as a means of conducting international relations. For that reason, the entire concept of a formal declaration of war is somewhat anachronistic. More frequently when the President commits troops to battle as was done in Vietnam and Afghanistan, a state of war exists although there was no formal declaration.