One of the things that stimulated US imperialism was the end of World War II, since the US emerged from the war the greatest superpower in the world--which allowed it to assert itself on a global scale in attempts to implement democracy.
Two things that challenged the confederacy were diseases and population disadvantage.
Diseases challenged both sides and killed more soldiers than the battles themselves.
The other challenge was that the North has more soldiers, because the North has more people. So the Confederates were outnumbered.
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He was passionate and committed to the course of farm workers, and provided unwavering front line leadership. He was also a clever strategists who employed networking skills a great deal.
The answer for this is A. The Congress-House of Representatives and the senate