The Crusades

Though in character they somewhat match the Crusades of our timeline, they are for a slightly different purpose. The Civilis of this world kept its Greek language skills and therefore its ability to read Greek vs. Latin, but they got greedy. They didn't just want to have the knowledge - they wanted to own it. And the best way they could think of to do that was to invade the Levant, the Middle East, and KMT and take those places from the Jews and Muslims. Factions of the Church of the Sacred Flame also fought with each other, believing their version of worship was a "truer" variety than others.