It would be the Tigris and the Euphrates. :)
Answer: the answer is B
Explanation: I got it right on edge 2020, hope this helped even if I’m late :D
The crusades were created by western European Christians after centuries of Muslim wars of expansion. To stop the expansion of Muslim states they had to reclaim christianity and the holy land in the middle east.
They enlisted black soldiers
There were already high tensions between the countries in Europe and the assassination led to ww1. They also were all in alliances with each other.