In our timeline, the two apostles of Jesus Christ, Peter and Paul, founded the Catholic Church in Rome. The Church formed small cracks in the Roman Empire and contributed to its fall. By this time, the Roman Empire had already served its purpose as a vector for Christianity. Christianity became the most popular religion in the world, but was split up into countless denominations.
But what if early Christianity assumed a more "assertive" stance? What if Saint Peter and the early Christian followers were militants, basing the Church in the Levant and conquering the region, much like Muhammad or present day ISIL, and continued to expand their theocratic empire? This alternate timeline explores the effects and consequences of a successful imperial Christianity in the Middle East.
The main Point of Divergence in this history is that Saint Peter is a different person. When he is appointed to plan and organize the Church by Jesus, he has something different in mind than in OTL. Instead of founding the Church in Rome, he plans to capture Jerusalem and become the Pope of an imperialistic Christian theocracy.