The event surrounding Jesus death did not become pivotal moments in human history until enough people were Christian. That is to say, Jesus only became historically important when enough people became Christians to make the sect relevant. That didn't happen in the Roman Empire until at least two centuries after Jesus' death.
The pivotal moment in history is the fact of the ressurection. It's relavance is neither enhanced nor deminished by the number of believers or lack thereof. The pivotal moment in an explosion is when it starts, not when it's noticed.
Hmmm?! Christ was IMMEDIATELY relevant to the Roman Empire - He claimed to be a King. In fact, all religions were tolerated by the empire except Christianity because Christians would not ascribed deified status to the Emperor. Paul and Peter were both killed by Rome specifically because they were Christian - Nero liked to set Christians on fire and eat by the light of the flames. Christianity was always important to Rome, and it evetually even took over the empire.