What groups of people do you think would be the most affected by the United States getting all this new land?

The Federalists

Explanation:

Federalists - a person who advocates or supports a system of government in which several states unite under a central authority.The Louisiana Purchase - The Louisiana Purchase was a land deal between the United States and France, in which the U.S. acquired approximately 827,000 square miles of land west of the Mississippi River for $15 million.U.S. Constitution - A document that embodies the fundamental laws and principles by which the United States is governed.

The Federalists
They opposed it because they suspected that new states formed in the Louisiana Territory would be Republican and thus jeopardize the balance of power. Some Federalists planned to secede from the Union.