Let's concentrate on others after this. So how many empires do we know that were ethnically and linguistically homogeneous? Rome had plenty of Emperors of other origins. Berber,Syrian,Arab,Balkan,Celtic origin/speaking emperors had all been there but they had the equal zeal towards the Roman Empire. Why can't we expect the same earlier in the Anatolia,Caucasus and the Fertile crescent earlier? We need to know that even in the Bronze age and the Iron age,the empires in this region were not as ethnically and linguistically homogeneous. All three Hellenistic Greek Kingdoms elsewhere took people and aspects from the Natives there. So,I don't think this necessarily holds true until there is an upheavel.
Which is completely true. If the king of one of these cities decides he doesn't want some other king to have a say in how he runs his city, then he gets an army sent to his doorstep and told to submit. That's empire building 101. Unfortunately, empire building is by nature pretty violent, which is often counterproductive to technological advancement. Spreading diseases, causing famine, brilliant young minds dying in battle, that's been a side effect of empire building since day one. Archimedes is a famous example of a scholar killed in warfare (granted, he was 75 years old).
That is what we want to avoid here. In this timeline,they would discover,for them, advanced Science and Technology in a faster manner and use it to generate more resources for survival,stability and advancement. In OTL,the Neolithic and Bronze age farmers dispersed away to other places from the Anatolia and Caucasus. But in this ATL,they stay back and build up the region and step by step neighbouring regions. Indo-Europeans,Hurro-Urartians,Neolithic Basque Like ethnicities,ethnicities like Isuarians,Sumerians,etc all come together and build cities and advanced civilizations instead of some dispersing as tribes and others building small city states. Systematically,after building up these regions with Mega cities dotting and quite rapidly advancing technology and hence huge populations,they start incorporating other peoples and bringing them in and developing all the lands as they spread.
But why? What reason do they have to stay behind and "build their region up" (and abstract concept that would make little sense to these people)? From their point of view, the land on the other side of that ridge, be it the Indus Valley, the Balkans, whatever, is great land and has few people. Where they currently live has lots of people, and the amount of farmland is getting low. "Nature abhors a vacuum" applies here. Further, Bronze Age cities had limitations, since there's limited amounts of water in the Levant, rivers shift course (hence all the abandoned ancient cities), and there's problems with soil salinity which all affect how big of a population you have. You will, at some point, run into a major drought, and odds are a drought will occur after years of poor crop yields due to soil salinity. Then your people will either die or disperse and cities will get abandoned.
And then why should their own technology not spread? Agriculture and farming spread to unrelated peoples before long, and so did bronze and iron. So now it's spread to their neighbours, and now their have no reason not to laugh in their face when they're told to submit.
And why is technology an inherent good if you're an ancient king? Sure, it's fascinating to anyone, as many centuries of automatons can attest to, but what practical purpose does it serve? Can it summon up more food or gold or instantly knock down the walls of a revolting city? Obviously not, and they have no indication that it will lead to anything like that since they can't just look at the tech tree to see what they need to research to get, say, cannons or dynamite. So why waste money on something like that when you could instead build monuments to your gods? After all, the gods can give your country more food and gold and knock down the walls of enemy cities no problem, so you better please them. Overall, a lot of this is counter to human nature.
Speaking about India,those who were primly involved in the building of Indian civilization,Indo-Iranians(Indo-Europeans) and the Neolithic migrants from the fertile crescent are already a part of the Union. So rather than an invasion,It would be a migration and migration to India isn't that difficult.
Except it would since no empire aside from the British ever ruled both India and the Levant (Alexander and the Mongols tried and failed). Once they do go to India and "develop" India (which India would develop long before they ever even heard of these people), then India has no reason to stay around with them.