U.S.A,the “civilizing mission”

But what about ideological factors such as the idea of the “civilizing mission” or
Manifest Destiny? By the late 19th 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 19th and early 20th centuries?