Complex sentence: He was appointed by Napoleon Bonaparte to be colonial prefect (governor) of Louisiana in 1802, and arrived in the colony on March 26,1803, just two weeks before Napoleon made his decision to sell Louisiana to the United States.
Split into simpler sentences: He was appointed by Napoleon Bonaparte to be colonial prefect (governor) of Louisiana in 1802. This was just two weeks before Napoleon had made his decision to sell the Louisiana colony to the United States.