Excerpts from Books and Wikipedia
"In 1697, 15-year-old Charles XII came to the throne. Sweden’s chief victims over the previous century--Denmark, Poland, and Russia--sensed an opportunity to take advantage of the inexperience and youth of the new monarch. The result was the Great Northern War: Denmark invaded Schleswig-Holstein, Poland attacked Riga, and the Russians invaded Livonia. Unfortunately for them, Charles XII turned out to be a military leader fully as talented as his ancestors. Now 18, he personally led the Swedish army in a counterattack, first defeating Denmark, then the Russians, and finally embarking on a brilliant campaign in Poland that lasted several years and produced at least six major victories. Charles XII’s personal role model was Alexander the Great. Well aware that Alexander had conquered a vast eastern empire with a relatively small army, Charles now determined to invade Russia and capture Moscow. The army with which Charles proposed to do this numbered around 40,000. On September 7, 1707, Charles and his forces crossed the Oder River into Poland. His opponent was another young, determined ruler: Peter I of Russia . . ."