For several hundred years the Tatars raided almost yearly deep into Ukraine, Muscovy, Poland, Lithuania and the Danubian area.
These raids were launched specifically against Christian peoples, which the Muslim Tatars viewed, in agreement with Muslim orthodoxy, as their legitimate prey.
You may not consider this terrorism, but I suspect the people most affected would have disagreed. Estimates vary wildly, but range upwards of 3M captured and sold into slavery, with many no doubt killed in the process not included in these numbers.
The Tatars themselves considered their raids to be jihad. Modern terrorists consider what they do to be jihad.
Since the harvesting of the steppe was aimed intentionally at civilians, not with the goal of defeating armies or conquering territory, it seems to me to pretty clearly meet most of the criteria for what we today call terrorism.
To the best of my knowledge Tatars had political motives. They did not spread jihad. And definitely they weren’t terrorists. These were normal territorial wars. Calling to fight “against christians” had different conotations than today. Yes, it was violence as every war is. But these were periods of formation of states in that region. I would like to repeat that overall experience in Eastern Europe of coexistance with Muslims is not negative. Central and Eastern Europeans were not oppresing them but to the contrary trying to help them be educated and merge into the society. I think we can compare early period of wars to the time of maturing. However today there is no excuse to come back to such primitive culture. The problem is, this is dr Jasser point as I understand it, that radicals are trying to have renewal of this Middle Ages practice. But not everyone is radical. Bernard Lewis makes good distinction between them and moderates.