An interesting argument from scholar Patrick Fitzsimmons that what ended the Bronze Age was not a better substitute for bronze but a cheaper one:
The Bronze Age collapse — as this sudden disappearance of regional powers is known — is one of the great mysteries of ancient history. The usual explanation points to a series of catastrophes around 1200 BC: droughts, mysterious invaders called the Sea Peoples, famines, and internal revolts. . . . The question is not why the Bronze Age empires fell, but why, after they fell, nothing like them returned for centuries. Why did it suddenly become so hard, seemingly, to build and sustain an empire? . . .
Bronze is an alloy of copper and tin, and the tin in those bronze weapons would have had to have traveled thousands of miles from distant mines, perhaps in modern Afghanistan or in Western Europe. The difficulty involved in mining and transporting tin is one reason that access to bronze weaponry remained concentrated in military and elite institutions. The average citizen still largely relied on tools made of copper, stone, bone, or wood. But just a few centuries after Kadesh, ordinary Hittite and Egyptian farmers had access to a new material: iron.
Because iron could be produced locally, imperial centers no longer had such a strong advantage over their subject peoples. The invention of iron weaponry meant the political equilibrium was forever changed.
Read the whole thing; there’s a lot more detail. There are two military truths here worth remembering. One is that the most elite weapons are not always the most useful. The American Sherman tank or the Russian T-34 were not as powerful, or in some cases as well armored, as some of the best tanks of Nazi Germany, but they were mass-produced because they were designed to be cheap and easy to make. The Second World War, the Civil War, and any number of Western wars against non-Western foes were won in good part not because of more or better soldiers or higher-tech equipment but because one side could build and replace good-enough weapons at scale and with speed.
The other truth, which Fitzsimmons notes, is that advances in cheap military technology can erode the advantage that professional armies have against insurgents, non-state actors, and smaller foes. That can be bad for American military hegemony, but it can also strengthen the depth of our own defenses.