Things you should know:

Islam spread far from its birthplace in the modern nation of Saudi Arabia.  By AD1095, Muslim territory included land where Jesus Christ lived.  Christians warriors of the era believed Christians, not Muslims, should control their holy lands.
The Crusades were a series of wars initiated by Christians to win back their holy lands from Muslims.
The Crusaders were ultimately unable to reclaim their holy lands, but the wars had another effect: Western Europeans had left their homes to fight in a distant war.  The stories of the returning Crusaders encouraged their countrymen to look beyond their own villages for the first time.

The Turks and the First Crusade

     The modern nation of Turkey is named for its Turkish inhabitants, but the Turks were not originally from Turkey.  The Turks were nomadic people from Central Asia.  Many Turks remain in that area, in fact, there is a nation in Central Asia known as Turkmenistan (“land of the Turks”).

      One Turkish tribe, the Seljuks, began moving into the Anatolian peninsula, or what we now call Turkey.  These Turks were Muslims, and a Christian emperor, Alexius I, controlled the peninsula. Alexius appealed to the Pope to help him rid Anatolia of “the unbelievers.”

Pope Urban II received Alexius’s call for assistance, but decided to use that call to advance a more ambitious plan.  Jerusalem, on the east coast of the Mediterranean Sea in the modern nation of Israel, is considered holy land to Christians, Jews and Muslims, but in 1095, the city was controlled by Muslims.  The message from Alexius presented Urban with an opportunity to retake the holy lands from the Muslims.  The pope called for a “War of the Cross,” or Crusade, to retake the holy lands from the unbelievers.

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Pope Urban persuaded the knights of Europe to join the Crusades

Urban appealed to the knight's religious convictions
Urban said Muslim Turks were robbing and torturing Christian pilgrims journeying to the holy land.
The war offered knights a chance for glory and wealth.
Urban suggested the knights fight Muslims instead of continuing to fight one another.