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........

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