The Crusades were a series of Human wars conducted by European noblemen to reclaim some of the former Roman Imperial territories along the Eastern Mediterranean seaboard which had been lost to the advance of Islam. Some of these territories had special significance for the noblemen's Christian religion.
Q remarked in 2369 that Earth was a lot more fun during the time of the Crusades - that is, the last decade of the 11th century, again in the mid- and late-12th century, and through most of the 13th century. (DS9: "Q-Less")
When the Hirogen transformed big parts of the USS Voyager into holodecks in 2374, they recreated many conflicts including the Crusades, in which Seven of Nine was badly wounded. (VOY: "The Killing Game")
|Earth wars prior to the Federation|
|Crusades • American Revolution • American Civil War • World War I • World War II • Brush Wars • Earth Cold War • Eugenics Wars • World War III • Earth-Kzin Wars • Xindi incident • Earth-Romulan War|