For Christian dominated Western Europe Islam represented an frightening wave that threatened to dominate the continent. Though the initial influx was repelled at the Battle of Tours, the stage was set for a centuries-long conflict. The Crusaders’ attempts to recapture Jerusalem led to endless, often inconclusive wars.
Despite the on-going conflicts, another facet of Islamic culture contributed directly to the rich intellectual life of the High Middle Ages. Muslim scholars transmitted the core of classical Greek and Roman philosophy, science, and literature to Western humanists. A very good documentary gives an overview of the complexity of the Muslim world.