Considered controversial at the time, the Louisiana Purchase added a vast amount of territory to the relatively new nation of the United States. The purchase itself had major impacts that rippled through American society. This chart shows the total amount of US territory expansion with the Louisiana Purchase.
The Louisiana territory was a vast amount of land west of the Mississippi River that historically had been claimed by the French. Through a series of treaties the land changed hands a couple times, though by 1803 it was owned by France once again.
Around this time the US became nervous that their access to the port city of New Orleans was being threatened. The Americans needed this port, and the access to the Mississippi River, to transport goods from their adjacent territories to overseas markets. New Orleans was one of the few ports the Midwest could ship good out of prior to the Erie Canal.
US Territory Expansion with Louisiana Purchase
In 1803 president Thomas Jefferson sent future president James Monroe to France to settle their worries through diplomacy. Jefferson authorized Monroe a sum of $10 million to attempt to purchase the city of New Orleans, Florida and as much other territory as he could get. Accomplishing this would quell their worries in the region for the time being.
When Monroe arrived, he found a different offer on the table from France: the entire Louisiana territory, including New Orleans. Wary of another war with England and bogged down by slave revolts in the Caribbean, Napoleon saw the Louisiana territory as more trouble than it was worth. He did not want to have to spare troops to defend the region should war break out in Europe again.
After weeks of negotiations, Monroe secured the entire Louisiana territory (~827,000 sq miles) for a sum of $15 million. After Congress ratified the treaty later that year, the land nearly doubled the size of the United States. It was a monumental turning point in US history.
The negative side of this treaty was that it encouraged further encroachment into Native American territory. Tensions remained high as settlers demanded more and more land. Eventually, these tensions would boil over into the Trail of Tears.
The only other territorial acquisition prior to that had been that of the Vermont Republic in 1791. This land was disputed, as the state of New York claimed rights to it, though Vermont had claimed its own independence from the US and Britain and even drafted its own constitution. In 1791, the republic finally agreed to join the United States as the state of Vermont.