Jumping in a little late...
Hello all.
First off, nice to meet you. I'm new here.
Some of this might be redundant, but if it is, consider it advocacy for those who have said it before.
As for the most important change -Christianity- I have a few facts here.
A pretty reliable estimate of population and Christianity's profusion I found in a book called "The Rise of Christianity" by Rodney Stark, a sociologist. He posits that the population of the empire as a whole is generally agreed by most scholars to be around 60 million at this time. Even at a growth rate of FORTY percent per decade since Christ, Christianity would still only have approx. 6.2 million converts, or 10.5% of the population.
Someone pointed out that the distribution of these people would be an important factor. I agree. A majority would have been in the east, and most would have been in urban areas.
Now if Constantine hadn't come along...would Christianity still have "triumphed"?
Difficult to say. For the most part I agree with several of the statements here:
IMP CAES AUG:
"Or equally, none of them. It is easy to forget that Christianity was pretty much the only active proselytizing religion of the time that could not fit comfortably within the larger structure of Graeco-Roman paganism."
Yup. No one else was actively looking for converts. And, likewise, most could syncretize. Christianity is exclusive, so it is very surprising that it was adopted.
Lysandros Aikiedes:
"The Christians did not have such a large following, but they were quite organized and hierarchal, so Constantine may have saw some use in that. Also just because its said to have "appealed to the lower classes of the empire", doesn't mean that every slave or pauper wanted to join them. "Salvation" in the Christian sense was an alien concept to Pagans."
Correct. If you think about the effect of Constantine's conversion and the subsequent ADOPTION of the religion, you kind of get a top-down conversion scheme. Not grassroots. Despite the appeal of salvation, the concept was indeed alien.
CHRISPI:
"While Licinius was more tolerant of Christians than Maxentius or Maximinus, it doesn't mean that he was sympathetic to them."
Yes. I think people look back on the events leading to Christianity and they seem inevitable and preordained. But the fact is, persecution was on and off since the beginning. It was not as if these edicts were heralding a new age where the Romans saw the writing on the wall. In fact, Licinius reneged on the Edict in 320, renewing persecutions. [Inicidentally, this served as a cassus belli for Constantine.]
With all that said, I think it is fair to say that, historically speaking, Constantine's actions as an emperor make him something of a loose cannon on par with Diocletian. Romans, as a general rule, do not take well to radical change. Compare the image of Caesar and his fate to that of Augustus and his.
Both Diocletian and Constantine did, in the OTL, affect radical changes, and they were successful (Diocletian's only briefly, of course). BUT, these were drastic times, and I think that is why the aristocracy et al was receptive. Also, at this point, the Emperor was a much more autocratic figure.
But I think that the Romans would be perfectly happy with an Emperor who DIDN'T rock the boat just the same. They are traditionalists, for the most part.
Here is my argument:
The Roman civilization historically adapted to change by retooling its existing system. The Republic was seen as a devolved Monarchy, the Principate was a palatable fiction of the Republic, the Dominate was a recognition of the authority of imperial power and dropped the pretense of republicanism altogether.
I would think that the "natural" course for the Roman system at this point would be to continue moving forward. The emperor was already seen as semi-divine at this point. The imperial cult had existed for centuries. Constantine associated himself, as many before him had done, with Apollo or Sol, etc. etc. In many other contemporary nations besides, monarchs were often treated as divine. It seems to me that Rome could easily have slipped into that path. Indeed Constantine did, in some ways, appropriate divinity by claiming to be sponsored or protected by Christ.
As for the immediate political landscape of Constantine's death/loss:
He was an amazing general. When he defeated Maxentius, it was against pretty long odds. And the entire period of the Wars of the Tetrarchy was just a damned mess. Alliance and counter-alliance, back and forth. The empire was in fourths (sometimes more), and the alliances made a checkerboard of it. Without Constantine to defeat everyone and unite everything, I think that the wars go on slightly longer, but in the end nothing is reunited. So in effect the Tetrarchy is a "failure" but doesn't collapse, per se. That is, the system didn't quite work as planned, but the empire is, at least for a while, split into parts that are -at least theoretically- more defensible and manageable.
The questions are:
With Constantine gone, which tetrarchs or usurpers will be left standing? Who has the potential? Do the emperors even want to fight each other or was Constantine just that greedy?
Which empires have any possibility of long term survival?
Several capitals already exist (Trier, Milan, Sirmium, etc.); are they enhanced as Constantinople was in OTL? [I don't think they would be to that level, Constantine was rather megalomaniacal in that sense.] Keep in mind that Maxentius was a prodigious builder. Constantine's basilica was actually built by Max. And it is known that Max. attempted to increase fortifications in Italy and improve his corner of the empire.
As far as religion, can a Tetrarchy claim to be vicars* of a single-god system (assuming any other emperor besides Constantine had any desire to embrace something like organized monotheistic religion)? Henotheist or whatever it is.... (Think a "college of popes"...not unlike the flamines. The idea of collegiate political and religious office are well-engrained and go hand in hand in Roman culture, so it is possible.)
Sorry for the long-winded post. Hope I didn't miss anything.
The reason I say this is because Constantine, as sole representative of God on Earth, couldn't very well be one among equals. So the other emperors had to go in order to justify his claim. One god. One emperor.
If you have a tetrarchy, how does that work?