Christianity stood at the cradle of Islam, or more exactly, it constituted one of the components of Islam. The connection between Islam and Christianity became more and more intertwined, and that these two great religions have passed through all phases of human relations—through aggression and defence, through respect and toleration, enmity and friendship. The Crusades convinced Islam of the aggressive qualities and potent danger of European Christianity, and of the hate and hostility of the Christians towards them. Martin Luther was deeply interested in developments connected with Islam, but he cherished no hopes for its reformation, nor did he envisage the idea of mission work among Muslims. Islam tried to close its doors as long as possible, because it felt instinctively that the new Western way would ultimately destroy all its ideals. Protestant missionary societies, mostly sponsored by British-, American-, or German-sending organizations, entered the countries of Islam.