OTL: The year is 1700. The Battle of Narva has just taken place. The Swedish army, with the strategic use of a blizzard, has cut the Russian army in half, and sent the invaders packing.
POD: Peter I does not leave to Moscow days before. He stays to lead his army. Swedish King Charles XII decides agree to Poland-Lithuania's mediation between him and Augustus II.
ATL: Among the thousands of Russian casualties, the lifeless body of Peter I lies in the snow. Not only is Russia's leader dead, but her army is retreating. Peter the Great's heir, Alexei Petrovich ascends to the throne at age 10. Alexei, who finds the Great Northern War nothing more than two kingdoms' greed, agrees to surrender claims in the Baltic Sea along with a large sum of money found in the Treaties of Moscow. The war ended, leaving scars on Russia never to heal and Charles XII arbiter of Europe. Within the year, Alexei is assassinated after making decisions that lead Russia into poverty.
That changes basically all of modern history. Russia never becomes a great power (no Russian Empire, no Soviet Union), and the Swedish Empire continues on. Perhaps it continues on to World War I, and takes on the role of Russia in the original timeline; could become Communist later on. Could you a Communist Sweden?