The first recorded history of the Laos begins with the unification of the country in 1353 by King Fa Ngum, who established his capital at Luang Prabang and ruled a kingdom called Lane Xang ("Land of a Million Elephants"). During the Vietnam War, U.S. bomber pilots returning from Vietnamese air strikes would empty their remaining bombs over Laos. They dropped 260 million cluster bombs between 1964 and 1973, or the equivalent of a fully-loaded B52 bomber's cargo dropped every eight minutes for nine years. More bombs were dropped on Laos than were dropped worldwide during World War II, thus Laos became the most heavily bombed nation in history. It has yet to recover fully.