The Crusades were started when Muslims took over the "holy land" of Jerusalem. The Christians wanted the land back so they sent attacks.
Pope Urban II called for people to help crusade and built a strong army. SO, in 1098, the crusaders laid siege to the city of Antioch in Syria for nine months before it fell to them. The following year they surrounded Jerusalem and fought their way into the city.
As Muslims band together, they fought against the crusader kingdom, they successfully captured Edessa, the capital of the most northern crusader kingdom.
Richard I of England led the third crusade to retake the holy land from the Muslim leader Salah al-din, who had recaptured much of Palestine. After forcing the surrender of the Palestinian town of Acre (as shown above), Richard's troops fought their way toward Jerusalem, but his army was not strong enough to attack the city.
Some effects of the Crusades were that Christianity was spread throughout the midwest and with that trade and ideas and technology.
In 1192, the two leaders signed a peace treaty allowing the Crusaders to keep some territory and allowing Christian pilgrims to enter Jerusalem.