World War II: US attacked by Japanese in 1941. Declares war on Japan. Germany declares war on US. US goes to war with Japan
Korean War: Communist backed North Korean Army invades South Vietnam. US invades
Vietnam War: Communists again! US backs South Vietnam in war to contain communism
Persian Gulf War: Saddam Hussein invades Kuwait. World not happy. Oil at stake. US leads UN coalition in.
Afghanistan War: 9/11 leads to a furious response against the Taliban. US stays and continues to fight after Taliban ousted for no real reason.