Complex sentence: In the early years of the French Revolutionary Wars, Frederick Francis I remained neutral, and in 1803 he regained Wismar from Kingdom of Sweden, but in 1806 his land was overrun by the First French Empire and in 1808 he joined the Confederation of the Rhine.
Split into simpler sentences: In the early years of the French Revolutionary Wars, Frederick Francis I remained neutral, and in 1803 he regained Wismar from Kingdom of Sweden. In 1806 the land was overrun by the First French Empire, and in 1808 he joined the Confederation of the Rhine.