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So, say Alexander the Great lives longer, finishes his plans to take over Arabia Felix and Carthage, and maybe, with new Persian troops, takes another crack at India and he at least gets some more of it, depending on whether Chandragupta, his unwitting protege, is his opponent for round 2. His sons grow of age and he has at least one competent one, and the Persian-Greek cultural merger he was imposing and the colonies he planted have more time to establish. His empire becomes the dominant empire of the ancient world rather than Rome, and lasts for some time until it collapses.

In this much delayed "to the strongest" scenario, say around 200 CE, what does this dark age look like? Considering much of its in Asia, steppe nomads would probably play a large role, Scythians, Huns, etc. I think with a less influential Rome, the Celts stay stronger and may be the ones sacking the Greek cities. Christianity would be probably butterflied, so maybe Buddhism or Zoroastrianism becomes the dominant religion in whatever Diadochi or barbarian successor states arise. Maybe a merely conquered and Hellenized Carthage makes a comeback without Rome razing it.
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