Why did Thomas Jeffereson want to purchase the Louisiana Territory?

Answer 1

It was obviously beneficial for the prosperity and success of the United States to be able to continue to expand westward across the continent of North America, and the Louisiana territory was the next step in doing so, at the time it was purchased. It could be argued that the US could have seized it by military invasion, rather than purchasing it, however the US had very good relations with France, which had assisted the colonists in their in the rebellion against Britain, and it was easier and even cheaper to simply buy the Louisiana Territory rather than going to war with France. So it was a very logical purchase.

Answer 2

Jefferson wanted to make America bigger, as well as gain the Mississippi River for western farmers.