How was the Young America Movement different from Manifest Destiny?

I would say that the two overlapped to some extent but
that the Young America movement was much broader in its scope of
concerns.

The idea of Manifest Destiny was really just
confined to the idea of expanding the United States.  It argued that the United States
was destined to spread itself over the whole continent.  This was based on the
superiority of American government, culture, and religion over those of the Indians and
even the Spaniards in Mexico.

By contrast, the Young
America Movement was interested in other things.  It was, for example, interested in
free trade and in increasing levels of democracy both at home and abroad.  It was also
interested in creating an American culture that was separate from that of Europe.  This
is a much broader scope of interest than the idea of Manifest Destiny
encompassed.