the coalition of the Kingdom of Poland and the Grand Duchy of Lithuania (later the united Polish–Lithuanian Commonwealth), the Kingdom of Sweden, and Denmark–Norway for access to the Baltic coast and sea trade. In 1572, an invading army of Crimean Tatars were thoroughly defeated in the crucial Battle of Molodi. The death of Ivan's sons marked the end of the ancient Rurik dynasty in 1598, and in combination with the disastrous famine of 1601–1603, led to a civil war, the rule of pretenders, and foreign intervention during the Time of Troubles in the early 17th century. The Polish–Lithuanian Commonwealth, taking advantage, occupied parts of Russia, extending into the capital Moscow. In 1612, the Poles were forced to retreat by the Russian volunteer corps, led by merchant Kuzma Minin and prince Dmitry Pozharsky. The Romanov dynasty acceded to the throne in 1613 by the decision of the Zemsky Sobor, and the country started its gradual recovery from the crisis. Russia continued its territorial growth through the 17th century, which was the age of the Cossacks. In 1654, the Ukrainian leader, Bohdan Khmelnytsky, offered to place Ukraine under the protection of the Russian tsar, Alexis; whose acceptance of this offer led to another Russo-Polish War. Ultimately, Ukraine was split along the Dnieper, leaving the eastern part, (Left-bank Ukraine and Kiev) under Russian rule. In the east, the rapid Russian exploration and colonisation of vast Siberia continued, hunting for valuable furs and ivory. Russian explorers pushed eastward primarily along the Siberian River Routes, and by the mid-17th century, there were Russian settlements in eastern Siberia, on the Chukchi Peninsula, along the Amur River, and on the coast of the Pacific Ocean. In 1648, Semyon Dezhnyov became the first European to navigate through the Bering Strait. Imperial Russia Under Peter the Great, Russia was proclaimed an empire in 1721, and established itself as one of the European great powers. Ruling from 1682 to 1725, Peter defeated Sweden in the Great Northern War (1700–1721), securing Russia's access to the sea and sea trade. In 1703, on the Baltic Sea, Peter founded Saint Petersburg as Russia's new capital. Throughout his rule, sweeping reforms were made, which brought significant Western European cultural influences to Russia. The reign of Peter I's daughter Elizabeth in 1741–1762 saw Russia's participation in the Seven Years' War (1756–1763). During the conflict, Russian troops overran East Prussia, reaching Berlin. However, upon Elizabeth's death,