Complex sentence: With the collapse of the Soviet Union, Ukraine was formed as an independent state in 1991 and most of the peninsula was reorganized as the Autonomous Republic of Crimea, while the city of Sevastopol retained its special status within Ukraine.
Split into simpler sentences: With the collapse of the Soviet Union, Ukraine was formed as an independent state in 1991. Most of the peninsula was reorganized as the Autonomous Republic of Crimea, while the city of Sevastopol retained its special status within Ukraine.