cause:louisiana purchase was completed

effect: napolean sold la to united states

Is that right?

You have the cause and effect turned around.

The U.S. bought the Louisiana Purchase from France.

Yes, that is correct. The cause of the Louisiana Purchase being completed was Napoleon's decision to sell Louisiana to the United States. The effect of this decision was the completion of the purchase, with the United States acquiring a significant amount of land, doubling its size.