what were the primary motivations and factors that led to the U.S. shift from isolationism and continental expansion to imperialism by the late 19th and early 20th centuries?

Using both primary and secondary sources–that answers the following question:

J.A. Hobson, a British theorist, and Vladimir Lenin, the Russian revolutionary and leader of the Bolshevik (later Communist Party) in the Soviet Union, both criticized late 19^th century imperialism as a capitalist conspiracy by “big business” to subjugate colonies for pure economic gain.  Colonies provided cheap raw materials and guaranteed markets for European and U.S. “trusts and monopolies”.  But what about ideological factors such as the idea of the “civilizing mission” or Manifest Destiny? By the late 19^th century, the U.S. joined other European powers in constructing an empire. The question is this: what were the primary motivations and factors that led to the U.S. shift from isolationism and continental expansion to imperialism by the late 19^th and early 20^th centuries? 

Must have a bibliography at the end.