What if the Roman Empire had collapsed in the 2nd century?

My understanding is that while Christianity may have been the largest religion in the Roman Empire by Constantine’s time, it was not a majority religion. If I recall correctly, it was estimated that about a third of the Roman population was Christian.

A further consideration. To what extent did the reunification itself inspire later people? It provided a real world example of a state that essentially fell apart but was then restored. Future generations could look at that example and think that however bad their current situation was there was a realistic possibility of returning to some past golden age. Without that example, the common belief might be that once a golden era ended it was lost forever and there was no point in looking back.

This may be true. I don’t think there are any adequate or reliable statistics about it. Nonetheless, it was already clear that Christianity was on the rise and probably would have continued to do so on its own. The various schismatic and heretical groups were already being weakened - partly because while Christianity was not directly favorable to Rome, they were almost all violent or barbarian or both.

Yeah, the Seleucids were long gone. They were rapidly losing territory from the very beginning. I had teacher who referred to it as “The Incredible Shrinking Empire.”

Anyways… as to the question, I think it would have slowed down Islam’s spread. I don’t know if it would have been stopped for good, but I would think it’s spread would have been delayed at least. I imagine the Persian Empire may have taken control of Anatolia and the Levant, and without a strong rival in Rome, they may have been better able to defend themselves. On the other hand, the lack of a strong military power at their door might also mean a smaller army and complacency in defense. So in the end… who knows?

In the Empire had fallen in the 2nd century, it’s an open question to what extent Christianity would have spread into Arabia, and without Arabian Christianity, would Islam have even developed?

I think to answer the question within the parameters of the OP’s assumed alternate history, we should look more closely at the specific threatss arrayed against the Roman empire in the mid-200’s; it isn’t enough to declare “The Roman empire fell in ~250AD”, we need to find a plausible path to its destruction at that time and from this deduce what the shattered pieces would look like.

The empire’s most serious military threat was from the Goths, who staged two somewhat successful invasions of Greece and the Hellespont in the middle of the 3rd century. Aurelian and the Roman armies were able to defeat the invaders (battle of Naissus) and drive them back north, but the province of Dacia (area north of the Danube) was permanently lost. We could assume (1) the Romans lost the battle and (2) the Eastern invasion along the Hellespont–which historically pillaged the Hellespont but didn’t do much permanent damage–was more successful. IMO this would have permanently cut of the eastern Palmyrene empire from Rome and allowed the Goths to plunder trade in the eastern Meditteranean. By no means should the Palyrene empire–largely the product of quicky conquest–be confused with the future Eastern Half of the Roman empire or the later Byzantine; IMO it would be much weaker and far more subject to internal squabbles and fighting. After, say, a century of internal war and skirmishes with the Goths, the area would be about on a par with the barbarian regions of northern Europe.

Turning to the West, one could imagine a similar scenario with the Gallic Empire–although here Postumus’ ability to fight off the barbarians was somewhat more successful. His death really signaled the end for the empire, as it descended into squabbling between the survivng generals. I could see the Gallic empire slipping much more quickly into feudalism as a result (assuming, again, Aurelian was unable to do much about it).

So we have two broken empires surrounding the military-defended shadow of the former Roman empire in Italy and perhaps North Africa. Trade in the West would likely continue, but the East would effectively be cut off (sort of a reversal of the actual fall in the late 5th century, which left the East intact but devastated the West).

I’m also going to assume these minimized forms of the Gallic and Roman empire would be far less effective in dealing with barbarian invasions as the restored Roman empire was, and assume the age of large geographical empires coming to an end around 350 ACE. By then they would be replaced by some type of early feudalism, but one much different than what was seen historically. The lack of Diocletian’s organizational genius and the binding power of an established Christian church IMO would cause a more ad hoc administration to develop, and IMO trade in general and the merchantile class in particular would be the only force strong enough to shape emerging forms of government in the West.

But that’s just my .02c…

In the mid-200’s the Roman empire was under intense pressure from the Sassanians under Shapur I. Palmyra by contrast was a midget.

I am not an expert on theology, Captain Amazing, but was not Islam also heavily influenced by Judaism?

I didn’t mean to imply Palmyra was a threat to Rome, rather that Palmyra would be the remains of the Roman empire in the East after the Goths/Germans cut off east from west at the hellespont.

I agree they’d be easy pickings for the Sassanians; there would likely be a far larger Persian legacy in Asia Minor and the Near East today…

Assuming that Islam develops in an otherwise similar matter (there’d probably be some theological differences because whatever Christian missionaries got to Arabia would represent a different mix of Christian sects, but perhaps that wouldn’t affect the military and political results all that much), it would have a harder time breaking out of Arabia. In our history, the newly united Arabs burst upon the Persian and Byzantine realms just as they were finishing a series of long and exhausting wars. Almost any alternative situation in which one or both empires are in decent shape would have slowed down or outright prevented the Arab conquests.

Islam is heavily influenced by Judaism, Christianity, and Zoroastrianism. A fusion of those traditions with the “pagan” Arabian traditions. With Allah, the patron god of Muhammed’s tribe equated with Yahweh. I would call Islam the very definition of Syncretism. I think that without Christian influence, it still would have come to be, just in a slightly different form.

Muhammad was fuzzy on the difference between Judaism and Christianity. According to Islam: A Short History, by Karen Armstrong, Muhammad did not learn until late in life, and much to his surprise, that Christians did not consider themselves a Jewish sect.

^
He did not become a Prophet until he was 40. Its interesting that his entire career takes place roughly at the time of the final great war between the Roman and Persians. A war that caused the whole balance in his area to be upset, they lived on trade with Syria; something that was cut off because of war. In addition, the Arabs had been on the frontline of the Rome v Persia rivalry for 700 years at the time, they had extensive dealings with both sides, some tribes supported one side, some the other. Its in that dynamic Muhammad grew up. Now if you have a situation where the Rome v Persia issue finished 300 years before he was born; well history is going to be very different.

True believers have the occupational hazard of finding themselves conscripted everytime a war begins, I would stay an “infidel” and pay whatever taxes to avoid that.

And incidentally, Iran remained mostly Zoresterian until several hundred years AFTER the muslim conquest. The Ummayads discouraged conversion, the Abbassids were fairly neutral about it, the Mongols killed everybody.

This is very true. The last major Roman internecine conflict was between a group of pagan senatorial holdouts in Rome and the Eastern Christian emperor Theodosius just a decade or two before the collapse of the Western Empire began in earnest when the Germans broke the Rhine barrier is 406.

Tried to add this to my previous post, but the time limit expired:

As for what would happen if the Roman Empire as a cohesive unit had collapsed in the second century, I think that most likely the post-Roman period would’ve seen less of a drastic decline in living conditions as what eventually came to pass in the 500s, if only because the Empire would’ve broken into various successor states (like the Greek imperial states after Alexander) instead of being wiped out by a foreign invasion (and while some might shake their heads at describing the Germanic migrations of the West as a foreign invasion, that’s more or less an accurate term, since the West’s governance was destroyed and replaced by foreign institutions that became the basis for the feudal kingdoms, and if that can’t more or less be called an invasion, what can?). Although this raises the question of what sort of effect the great “barbarian” migrations during the fourth and fifth centuries would have on a collection of smaller but more cohesive successor states than the vast and stretched-thin Western Empire.