Complex sentence: Its European portion, which occupies a substantial part of continental Europe, is home to most of Russia's industrial and agricultural activity and is where, roughly between the Dnieper River and the Ural Mountains, the Russian Empire took shape.
Split into simpler sentences: Its European portion, which occupies a substantial part of continental Europe, is home to most of Russia's industrial and agricultural activity. It was here, roughly between the Dnieper River and the Ural Mountains, that the Russian Empire took shape.