What happened in 1867 that allowed the United States to expand its territory

In 1867 the United States purchased Alaska from Russia, resulting in a great territorial expansion. On top of being a great territorial expansion, many americans praised the acquisition as a mean of weakening both Russia and England as potential rivals to American commerce in the Pacific.

The treaty that ended the war gave the United States a vast stretch of land from Texas west to the Pacific and north to Oregon ... The United States then owned all the territory of its present states except Alaska (purchased from Russia in 1867) and Hawaii (annexed in 1898)./

the continued presence of American troops increased further and a total of 475,000 were serving in Vietnam and the peace rallies were multiplying as the number of protesters against the war increased.