Land. Lots of land.
The Louisiana Purchase of 1803 intensified American migration to the west that was already well underway. Anglo-American settlement in the 18th century had largely been confined to the eastern seaboard. It made its boldest inroads where rivers allowed easy internal transportation. As a result the chief population centers of early North America were clustered on the coast or along its major inland waterways.
Answer:
A I think, though I might be wrong.
Explanation:
This is Spanish............................................
It is not so much unique but it was a huge impact because even though the U.S. tried to help out South Korea it end up with a so called agreement . There was never a treaty signed it just came to any agreement that each side should stay on their own side .