Why did President Thomas Jefferson choose to make the Louisiana Purchase?

Thomas Jefferson, the 3rd President of the United States, knew Americans were already looking beyond the Ohio River Valley in their push westward. France owned Louisiana which in 1800 extended from the present state of Louisiana north and westward all the way to the headwaters of the Mississippi and Missouri Rivers.

Early maps of the Louisiana Territory are purposefully vague as to where they end. France, England and Spain had vague, on-paper claims to what became the Oregon Territory, but none of them made a serious effort to explore or settle it. After the Louisiana Purchase, America was in a good position to do precisely this.

Jefferson had Congress's blessing and money to offer Napoleon a million dollars for the city of New Orleans. Napoleon, in need of quick cash to continue a war with England, made an intriguing counter-offer: the entire Louisiana Territory for $10 million. Jefferson took the offer (without waiting for congressional approval, a tactic that continues to echo to the present day).

At the time, America had two political parties, the Democratic-Republicans (Jefferson, Madison) and the Federalists (Adams, and possibly Washington, although he was loath to declare a party affiliation). One issue that divided the parties was whether American foreign policy and trade should center on England or France. The Federalists, even during the war, intended England to be our main trading partner all along, but Jefferson favored France and considered himself to have been the inspiration of the French Revolution.