The Crusades: A series of European Christian invasions of the Middle East, aimed at driving Muslims from the "Holy Land" of Palestine.
Generally history lists nine Crusades, beginning in the late 11th century and continuing into the 13th century. However, there were numerous smaller expeditions throughout that period and later. In fact, the last knightly order of Crusaders, the Knights Hospitaller, was finally defeated in 1798 at Malta... by Napolean Bonaparte!
Although the primary purpose of the Crusades was to capture Jerusalem and the Holy Land from Muslims, the Crusaders also massacred Jews, Orthodox Christians, and even Catholic schismatics or political opponents of the Pope.
The Christians did not succeed in taking and holding Palestine, but they did bring back knowledge of Middle Eastern and Asian technologies and inventions to Europe. They also engendered a lot of resentment and ill-will in the Middle East, a reasonable reaction to several centuries of repeated and bloody invasions.
The word "Crusade" comes from the Latin word crux or "cross," the symbol of Christianity.
"The Fourth Crusade never made it to the Holy Land; the Crusaders sacked Christian Byzantium instead."