If Ceasar had not crossed the Rubicon, the Empire would have fallen far sooner. At least, that was my distinct impression after working my way through Gibbon and a bunch of other works. (He always gets blamed for destroying the republic, but the republic was effectively dead at least 100 years beforehand. The Patrician-Plebian divides were growing apace. I don't see much reason to think it could have lasted as a republic that much longer). Without imperial control, Rome would have had a lot tougher time holding onto territory and keeping the various Goths, Ostrogoths, Sycthians, etc., at bay. I suspect it'd have fallen far sooner, perhaps even before establishing a solid eastern section.
And if the Empire had fallen far sooner (I'd guesstimate maybe 100 AD), there's a good chance that Christianity would not have spread anywhere near as widely, and thus, any "Jesus" - historical or imagined - would not have nearly as much impact.
It's a fair point.
Well, not just that. Pagan-Christian strife between citizens was its own problem, as well. But yes, it was a political move. (ie, so too was the Council of Nicea and the decision to side with Athanasius).
