The Olympic Games were suppressed, either by Theodosius I in AD 393 or his grandson Theodosius II in AD 435, as part of the campaign to impose Christianity as a state religion. The site of Olympia remained until an earthquake destroyed it in the sixth century AD.
Huge resources were spent on holding the games by the Greek rulers. The games were a gift to the common people. Hence, the fans did not have to pay to watch the games. Once the Christians took over the city of Greece, they decided to use the resources to bulid places of worship and spread Christianity. Christians did not view fighting as a Christian ideology.
From : http://answers.yahoo.com/question/index?qid=20090429011705AAIiONk