Early Christianity focussed on a hoped for 'kingdom' centering on the return of Christ. When that did not happen in the expected time, the focus changed to everlasting soul-life in heaven.
Althouth this is a popular view, there's really no substance to it. Recall that Jesus spent 40 days with his disciples teaching them the mysteries. Given the prophecies put forth by Jesus and his apostles, such as the destruction of Jerusalem, the dispersion of Judah to the four corners of the earth, a long period of apostasy that would last some 1260 years (Rev. 12:6), the fall of the Roman Empire and the establishment of independent nations, some strong and some weak (Daniel 2). They then wrote about a time of the "restoration of all things" (Acts 3), the restoration of Judah to the land of its inheritance, the rise of a Gentile despot called "the Beast," and his invasion of Jerusalem with a vast army (Rev. 11, Zech. 12-14). Then, after a fierce battle for the beleaguered city, Jesus appears and descends upon the Mount of Olives with ten thousands of his saints, he destroys the Beast and his army, sparing only a sixth of them. This is the true story of Armageddon.
The apostles knew all of the above because Jesus told them and they passed it on. It really wasn't something that could occur in their lifetimes. Jesus also told them that they would be killed and that wolves would enter the church not sparing the flock. Just before the Romans marched on Jerusalem, the apostles received revelation telling them to move the saints out of the city and into cities like Pella in the north, and they completely escaped the destruction of the Holy City.
Given that they understood prophecy, the Christian apostles knew all the things above had to be fulfilled. There's no way they could come to pass in their lifetimes, especially the 1260 years!
