Northern War, the name of two European wars.

First Northern War,
  • –60, was between Sweden and Poland. It was ended by the Peace of Oliva, by which Poland ceded Livonia to Sweden and East Prussia to Brandenburg., which had allied itself first with one side and then with the other during the war., was the chief beneficiary, as both Poland and Sweden were weakened.
Great Northern War,
  • –21, was one in which Sweden was defeated by several European powers. Russia wrested the eastern coast of the Baltic Sea from Sweden and became a major power.

The war began when Russia, Poland, Saxony, and Denmark combined against the Swedes. The 18-year-old Swedish king, Charles XII, quickly repulsed all his enemies. In 1704 he deposed King Augustus II of Poland. At the same time, however, Czar Peter I (the Great) of Russia conquered the Baltic district of Ingria and began construction there of his new capital, St. Petersburg.

Charles allied himself with Ivan Mazepa, chief of the Ukrainian Cossacks, and invaded Russia in 1708. His forces were routed at the Battle of Poltava (1709), and he fled to Turkey, not returning to northern Europe until 1714. Meantime Augustus recovered his throne and Russia seized Karelia, Estonia, and Finland. In 1715 Hanover and Prussia joined the alliance; they soon annexed Sweden's possessions in Germany. Charles was killed in 1718. In 1720 the exhausted Swedes made peace with all the belligerents but Russia by renouncing Sweden's German territories.

In 1721 the Swedes sued for peace with Russia, and under the treaty of Nystadt Russia retained all its conquests except Finland.