Explain how the spread of islam led to the crusades

Christians started the crusades in the past centuries. Christians usually organized them from the west of Europe. The purpose of the crusades, therefore, was to respond to the critics by Muslims to control Muslim spread that had occupied a large part of the land conquering pagan regions.

The launch this crusade however, led to the expulsion of many Christians from Syria. They, however, continued for many centuries but after some time, they were declined due to the formation of Protestants.

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the roman empire began to fall