The Great Northern War, fought from 1700-1721, gets its name from the fact the war focused on the Baltic, but the battlefields extended into Germany and deep into Poland and Ukraine. Sweden was a military power with a small empire in the Baltic, while Russia was still a landlocked place, backward when compared to the rest of Europe, not very powerful, and highly xenophobic. The Poland-Lithuanian Commonwealth was still powerful, and the Cossacks were still free. Moreover, despite the fact the Ottoman Empire was weakened, it held sway in the Balkans and deep into Eastern Europe, and the Krim Tatars were still raiding into Ukraine, Russia, and Poland for slaves. 

The Great Northern War would involve the Ottomans and the Tatars as well.At the time, Denmark ruled Norway, and Saxony was ruled by the elector Augustus the Strong, who was also king of Poland (an elector was a ruler with a vote in the election of the Holy Roman Emperor in Vienna). Sweden was an absolute monarchy ruled by Charles XII, and Finland had been a Swedish territory for centuries. Sweden also controlled Estonia, Ingria (the region around the current city of St. Petersburg), most of Livonia and Pomerania, Karelia, and a number of places along the German Baltic coast. The king of Poland was also the grand duke of Lithuania.