Allah - the Mighty and Majestic - said:
"It is He who has sent His Messenger with guidance and the religion of truth, that He may make it prevail over all other religions, no matter how much the disbelievers detest it." [Al-Qur'an 61:9]
We are given the good tidings in this verse that the future is for Islam, which gain dominance, ascendancy and rule over all other religions. Some people may think that this was fulfilled in the time of the Prophet sallallahu 'alayhi wa sallam and the Rightly-Guided Khulafah and the righteous kings - but that is not the case. Rather, only a part of this true promise was fulfilled then - as the Prophet sallallahu 'alayhi wa sallam indicated:
"Night and day will pass away until Al-Lat and Al-'Uzza are worshipped." So 'Aishah - radhiallahu 'anha - said: "O Messenger of Allah! I thought that when Allah sent down: 'It is He who has sent His Messenger with guidance and the religion of truth, that He may make it prevail over all the other religions, no matter how much the disbelievers detest it,' that it would be complete. He sallallahu 'alayhi wa sallam said, "There will be of that what Allah wishes." [Related by Muslim (8/182) and also Abu Ya'la in his Musnad (Q. 216/2)]