The military history of the American side of the war involved different strategies over the years. The bombing campaigns of the Air Force were tightly controlled by the White House for political reasons, and until 1972 avoided the main Northern cities of Hanoi and Haiphong and concentrated on bombing jungle supply trails, especially the Ho Chi Minh Trail. The most controversial Army commander was William Westmoreland whose strategy involved systematic defeat of all enemy forces in the field, despite heavy American casualties that alienated public opinion back home.