Du Gamla, Du Fria!

The Great Northern War was a conflict between Sweden and a Russia-led coallition between 1720 and 1721. In it, the Russian forces won after a long fight, and Sweden had to give Karelia, Ingria and Livonia to the Russians. This was mostly because the Swedish allies left early in the war, and Russia had more allies than Sweden.

but what if:

  
 * Saxony had been part of the Swedish alliance,
 * and Poland was in a more stable state that it was on OTL?

Eventually, the Great Northern War ends in the disintegration of Prussia, Hannover and Denmark-Norway, and a great weakening of Russia with the loss of Karelia, Kola, and northwestern Russia. This brings to a further strenghtening of the Swedish Empire, and an eventual transformation of it into the world's superpower.