During the Mongol invasion of Europe, Mongol tumens led by Batu Khan and Kadan invaded Serbia and then Bulgaria in the spring of 1242 after defeating the Hungarians at the battle of Mohi and ravaging the Hungarian regions of Croatia, Dalmatia and Bosnia.

Having passed through Bosnian and Serb lands, Kadan joined up with the main army under Batu in Bulgaria, probably towards the end of spring. There is archaeological evidence of widespread destruction in central and northeastern Bulgaria around 1242. There are several narrative sources of the Mongol invasion of Bulgaria, but none is detailed and they present distinct pictures of what transpired. It is clear, though, that two forces entered Bulgaria at the same time: Kadan's from Serbia and another, led by Batu himself or Bujek, from across the Danube.

Initially, the troops of Kadan moved south along the Adriatic Sea into Serbian territory. Then, turning east, it crossed the centre of the country—plundering as it went—and entered Bulgaria, where it was joined by the rest of the army under Batu. The campaigning in Bulgaria probably happened mainly in the north, where archaeology yields evidence of destruction from this period. The Mongols did, however, cross Bulgaria to attack the Latin Empire to its south before withdrawing completely. Bulgaria was forced to pay tribute to the Mongols, and this continued thereafter.

Some historians believe that Bulgaria escaped major destruction by accepting Mongol suzerainty, while others have argued that the evidence of Mongol raiding is strong enough that there can have been no escaping. In any case, the campaign of 1242 brought the frontier of the authority of the Golden Horde (Batu's command) to the Danube, where it remained for some decades. The Venetian doge and historian Andrea Dandolo, writing a century later, says that the Mongols "occupied" the kingdom of Bulgaria during the 1241–42 campaign.