The decisive battle of the Great Northern War between Sweden and Russia was the battle of Poltava. That's located deep in the Ukraine, southeast of Kiev, between Cherkassy and Kharkov.
That seems like a strange place for a Swedish army, especially one based on the Baltic in Livonia (which encompasses Latvia and Estonia). One would expect such an army to march east to Moscow, or perhaps north to the newly-founded city of St. Petersburg.
Apparently Sweden's King Charles XII had led his army west across Poland, all the way to occupy Saxony (the home of the elected King of Poland), with the aim of making Poland a puppet state, then back east across Poland for an invasion of Russia via "Lithuania," (which then also included modern Belarus and parts of the Ukraine).
Did King Charles XII create a new "base" in southern Polish cities like Krakow and Lublin from which to draw supplies and reinforcements for what would then be a logical invasion of the Ukraine? Was he trying to conquer Ukraine on behalf of his new Polish allies? Or were the allies in question perhaps the Turks (natural enemies of Russia)? If so, were they supplying him across the Black Sea, and up the Dniepr River?
What was he doing at Poltava? Was he trying to "go around" the main Russian army and take Moscow from the rear? Basically it doesn't make sense for a Swedish army to be that far south, except possibly at the head of a "grand coalition" involving other countries.