How was the Louisiana Territory obtained from France?

Thomas Jefferson purchased it from Napoleon for 11.25 mil. with a down payment of about $3 million at a time when Napoleon was at war with the British. Livingston was the ambassador for Jefferson who brokered the deal.

It is known as the Louisiana purchase

In fact, the remainder of the purchase was financed by a bond issue, brokered by Barings London. Thus, the British (and Dutch) financed the purchased, and in so doing funded Napoleon's war against the British.