[PROJECT] History Lessons

The Mongols defended Rus' from the Germans, Lithuanians, and Poles. For example, there is a known fact: Alexander Nevsky formed an alliance with the Golden Horde (he was also a blood brother to Sartak, the son of Batu Khan). After Alexander's death, a knightly army approached Novgorod. The Mongols sent a small detachment there. The Germans, learning that the Mongols were in Novgorod, turned back and left.
Furthermore, the Mongols also defended Rus' from Timur, albeit less successfully, but nevertheless, they prevented him from causing significant damage.
So, the Mongols fully fulfilled their defensive function.