In this episode, a Kingdom will become an Empire and an Empire will vanish. Alliances will be made and broken many times over, and Bulgaria will find itself at a pivotal moment.
Below is a map of Bulgaria under the reign of Ivan Asen II and a map of the Battle of Klokotnitsa, between the Second Bulgarian Empire and the Empire of Thessaloniki.
Here's a video about the Battle of Klokotnitsa (you can turn on English captions)
Here's an episode of the Youtube channel History Time covering the Mongol Invasion of Europe which took place during this time.
And another video detailing the Mongol's western expansion, this time from Kings and Generals.
Lastly, one final video focusing more on the 1241 Battle of Mohi.