Muslim forces ultimately expelled the European Christians who invaded the eastern Mediterranean repeatedly in the 12th and 13th centuries—and thwarted their effort to regain control of sacred Holy Land sites such as Jerusalem. Still, most histories of the Crusades offer a largely one-sided view, drawn originally from European medieval chronicles, then filtered through 18th and 19th-century Western scholars.
In addition of the answer that was stated, also they failed to realize the audacity and ferocity of the Nazi Party and Adolf Hitler that started a new world war and large scale of exterminations for the dream future and living space. Also they failed to stop him in his genocides and large war crimes committed during the war.
