A Genghis Khan meme. One of the lessons of history is that invading Russia, especially in the winter, is a very bad idea. Poland tried it in the seventeenth century, Sweden tried it in the eighteenth, France tried it in the nineteenth, and Germany tried it in the twentieth century. All of those invaders got worse than they gave. Only the Mongols pulled it off, because they had the toughest army of the Middle Ages.