Catherine II ("the Great"), who ruled in 1762–96, presided over the Age of Russian Enlightenment. She extended Russian political control over the Polish-Lithuanian Commonwealth and incorporated most of its territories into Russia during the Partitions of Poland, pushing the Russian frontier westward into Central Europe, and thus making Russia the most populous country in Europe. In the south, after the successful Russo-Turkish Wars against the Ottoman Empire, Catherine advanced Russia's boundary to the Black Sea, defeating the Crimean Khanate. As a result of victories over Qajar Iran through the Russo-Persian Wars, by the first half of the 19th century, Russia also made significant territorial gains in Transcaucasia and the North Caucasus. Catherine's successor, her son Paul, was unstable and focused predominantly on domestic issues. Following his short reign, Catherine's strategy was continued with Alexander I's (1801–25) wresting of Finland from the weakened Sweden in 1809, and of Bessarabia from the Ottomans in 1812. While in North America, the Russians became the first Europeans to reach and colonise Alaska.