The Mongol invasions of Russia and Eastern Europe occurred first with a brief sortie in 1223 CE and then again in a much larger campaign between 1237 CE and 1242 CE. The Mongols, seemingly coming from nowhere and quickly gaining a reputation as the 'horsemen of the Devil', enjoyed victory after victory, and eventually got as far west as the city of Wroclaw in Poland.
This is a companion discussion topic for the original content at https://www.worldhistory.org/article/1453/the-mongol-invasion-of-europe/.