Why did the US seek to become a world power in the 1890?

US asserts itself as a world power because of her economic compatibility and military prowess. Further, US champions the cause of people fighting for democracy any where in the world. There was a balance in power with erstwhile Soviet Union. With their exit,US has become the lone world power. However, with the uprise of China who is flexing her muscles, she will be the toughest competitor of US in the near future both economically and strategically, to retain the world power title. However, since US fights for democracy and China is under communist regime, the choice is obvious for democratic and peace loving people all over the world.