Complex sentence: Catherine the Great (reigned 1762--1796) presided over a golden age; she expanded the state by conquest, colonization and diplomacy, continuing Peter the Great's policy of modernisation along West European lines.
Split into simpler sentences: Catherine the Great (reigned 1762--1796) presided over a Golden age. She expanded the state by conquest, colonization and diplomacy, continuing Peter the Great's policy of modernisation along West European lines.