Complex sentence: Prussia gained the southern parts of Swedish Pomerania in 1720, Buchholz (1999), pp.341-343 Pomerelia in 1772, and the remainder of Swedish Pomerania in 1815, when French occupation during the Napoleonic Wars was lifted.
Split into simpler sentences: Prussia gained the southern parts of Swedish Pomerania in 1720, Buchholz (1999), pp.341-343. It gained the remainder of Swedish Pomerania in 1815, when French occupation during the Napoleonic Wars was lifted.