Most of us have heard of the crusades when knights attempted to take control of Jerusalem. Though I would doubt that many of us have heard of the northern crusades. In the 1200s the pope sent knights to invade Russia and neighboring countries. The Pope wanted to bring Christianity to them.
One battle they fought was called the battle of the Ice in 1242. After a few defeats, Alexander Nevsky decided to lead the crusaders to fight in a place of his choosing. He led them to the frozen Lake Peipus, and out onto the ice. There he strategically tired out the crusaders, brought in archers, and finally chased off the crusaders. The crusaders did not know the land well and ran straight onto thin ice, that cracked and plunged them into the icy water. This battle resulted in a treaty where the crusaders agreed to leave Russian lands, signalling the end of the northern crusades. From history, we learn that invading Russia is never a good idea.