The defeat and decline of the Swedish Empire.
A young boy king had inherited the crown of the Swedish Empire, and his neighbors saw an opportunity to attack. To their surprise, young Charles XII of Sweden turned out to be a fearsome opponent who quickly repelled their assaults - and then sought revenge.
Augustus the Strong was determined to prove his might by defeated Charles XII on the battlefield. He gathered his Polish-Lithuanian forces, met the Swedes, and proceded to... lose. And lose. And lose. Then he got deposed and started a civil war which of course he also lost.
Flush from his victories against Poland-Lithuania, Charles XII of Sweden sets his eyes on an even greater enemy: Russia. But its ruler, Peter the Great, is no pushover: as the Swedish troops advance, he burns down the countryside and leaves them starving and exposed as a ferocious winter sets in.
Charles XII had gone to the Ukraine hoping for supplies and reinforcements, especially from the cossacks led by Ivan Mazeppa. But Peter the Great was hot on his trail, and had no intention of letting him off that easy.
Charles XII narrowly escaped the Russian pursuit, with help from the Ottoman Empire. But the weak points in his army had been clearly exposed. Northern Europe united against him - but of course, Charles XII responded by launching a fateful counter-offensive into Norway.