In the 1880's, the US passed an anti-Chinese policy, which banned all immigrants and the naturalization of Chinese citizens. The immigration dropped from 40,000 to under 50 in ten years. The US also passes an act to dissolve the Mormon Church and rids Mormon's of their land and other properties. While Indians were being pushed off their land and onto reservations, there was an act passed, the Dawes Severalty Act, which allowed Native Americans up to 160 acres of land in hopes to civilize them faster.
In the 1890's, the government "cracks down" on the Native American religious movement known as the Ghost Dance. Federal troops killed the Lakota Indian tribe's leader and 350 of its followers in effort to stop the Ghost Dance. The last gold rush happens in Alaska near Dawson City. Wyoming and Utah enter the union and Hawaii is annexed by the United States by the end of the decade.
And from 1900 up until around the first world war, President Roosevelt enables the Preservation of American Antiquities Act in effort to help protect historic sites (like the Grand Canyon) for posterity. Arizona, Kansas and Oregon give women the right to vote. Industrial works go on strike and demand better wages and working conditions. The Panama Canal is completed, and the United States finally enters in the first world war.