Here is a summary of the Crusades from the Encyclopedia Britannica:
“The crusades were…military expeditions, beginning in the late 11th century…organized by western European Christians in response to centuries of Muslim wars of expansion. Their objectives were to check the spread of Islam, to retake control of the Holy Land in the eastern Mediterranean…to recapture formerly Christian territories… Between 1095, when the First Crusade was launched, and 1291, when the Latin Christians were finally expelled…there were numerous expeditions to… halt or slow the advance of Muslim power.
“Approximately two-thirds of the ancient Christian world had been conquered by Muslims by the end of the 11th century…The Crusades, attempting to check this advance, initially enjoyed success… but the continued growth of Islamic states ultimately reversed those gains. By the 14th century the Ottoman Turks (Muslim imperialists) had established themselves in the Balkans and would penetrate deeper into Europe despite repeated efforts to repulse them.”