Industrial Revolution in general was probably the most important change between 3000 BC and 2000 AD, in my opinion. Before industrialism, regardless of what civ are you talking about and at what period, something like 80-90% of humanity was farmers, peasants, fishermen, hunters and gatherers. Vast majority was illiterate and not urbanised too. Before industrialism, logistics was terrible, most of humans never travelled far, communication was terrible, supply was terrible, army movement was incomparably slower... Industrial Revolution changed the way humanity works. Industrial Revolution was so massive change, that nations which adopted it had devastating advantage over those who didn't and were basically capable of doing whatever they wanted, regardlessly of numerical advantage of their pre-industrial foes. I fantasized about Civ game which turns IR into the major gamechanger, when once-powerful-empires may completely fall and small underdogs may dramatically rise, depending on each nation's capability to industrialize. Where once somebody researches IR it all turns into OOOOH MAAAN WE GOTTA CATCH UP OR WE GONNA DIE, an industrial race of manufacturing and efficiency. It would make late game quite dynamic, too.