Crusades

The Crusades was a series of military conflicts in Earth's middle ages. These conflicts were fought for religious reasons - namely by members of the Christian faith against Muslims and other groups on Earth.

Originally the crusades were intended to recapture Jerusalem and other territories - which over the centuries come into to Muslim hands. The first crusade was held in the late 11th century, from 1094 to 1099. For the next two centuries there was an entire series of crusades.

Saladin was a Muslim general whose forces recaptured Jerusalem from the crusaders in the 12th century. Approximately 1000 years after his death, Starfleet named the Saladin class starships after him. (TOS manual Star Fleet Technical Manual).

Q once remarked to Vash that Earth was a much more fun place during this period in history. (DS9 episode Q-Less).

Captain Kathryn Janeway discovered that Fury society was ordered similarly to those in existence on Earth during the time of the crusades. (VOY novel The Final Fury).

When the Hirogen captured USS Voyager (NCC-74656), they used the ship's holodecks to study the races of the United Federation of Planets, whom they considered prey. One of the early simulations was one that took place during the crusades on Earth. The Doctor remarked to Seven of Nine that she should've seen herself after being sent after the crusades. (VOY episode The Killing Game, Part I).