Thus, Nixon (or his successor Gerald Ford) was unable to fulfill his promises to Thieu. At the same time, aid to North Vietnam from the Soviet Union increased. With the U.S. no longer heavily involved, both the U.S. and the Soviet Union no longer saw the war as significant to their relations. The balance of power shifted decisively in North Vietnam's favor, and the North subsequently launched a major military offensive, the Ho Chi Minh Campaign, against the South that culminated in the surrender of the Republic of Vietnam to PAVN forces on April 30, 1975.