I do not think that the US should have been imperialist in 1900. Doing so would have undermined everything that the constitution stands for; individual liberties. Just having gone through a war with ourselves over individual freedom, it would have been very hypocritical. Fighting off opression and then turning around and opressing another country was not what America was about. The US also had just gone through an industrial revolution, so the US had factories and sufficient resources to sustain themselves. There was no need for the U.S to be imperialist and it would have gone against what the Constitution was based on, individual freedoms.
Sources: my head, Eyewitness to History, p. 318
http://mossiso.com/2010/10/09/british-imperialism-and-gender-issues.html