Please explain the circumstances surrounding the Louisiana Purchase.What events occurred that led to the Louisiana Purchase?

After the Revolutionary War, Americans began to settle in
the Ohio River valley.  The Appalachian Mountains made it very expensive and difficult
to transport goods to the east coast.  The cheapest way to ship goods to the coast was
to float them down the Ohio River, then down the Mississippi River to New Orleans, where
they could be transferred to ocean going vessels for shipment to the east coast and
Europe.  The problem was that the U.S. had no control over New Orleans and Thomas
Jefferson, president at the time of the Louisiana Purchase, feared that the U.S. would
lose its right of deposit at New Orleans.  At the time, Louisiana was controlled by
Spain, but in a secret agreement, Spain was to cede Louisiana to France in exchange for
a Spanish Kingdom in Italy.  With knowledge of this agreement, Jefferson sent Robert
Livingston, and then James Monroe, to France to negotiate the purchase of New Orleans
from Napoleon for $10 million. With the hopes of a Caribbean empire based on the sugar
trade dashed with the loss of Santo Domingo, Napoleon lost interest in controlling
Louisiana. In need of money to continue his European wars, Napoleon offered the U.S. the
entire Louisiana territory, more than 800,000 square miles, for $15 million.  One
problem confronted Jefferson.  He was a strict constructionist and did not see anything
in the Constitution which would give him the power to purchase Louisiana.  What he did
know was that he did have the power to negotiate treaties. Knowing that this deal was in
the best interest of the United States, he put the purchase of Louisiana in a treaty
which the Senate later ratified.  In 1830, the United States doubled in size with the
purchase of Louisiana from Napoleon for $15 million.