Complex sentence: After the Treaty of Nystad in 1721 eastern parts of the Viborg and Nyslott County and the Kexholm County were ceded to Russia; and the rest was incorporated into the Kymmenegård and Nyslott County.
Split into simpler sentences: After the Treaty of Nystad in 1721 eastern parts of the Viborg and Nyslott County and the Kexholm County were ceded to Russia. The rest of these counties were incorporated into the Kymmenegård and Nyslott County.