I was reading that bronze age civilizations like Assyria and Babylon had to trade long distances to secure tin, since it wasn't often found next to copper so as to make bronze. I noticed that Spain appears to have both - copper in the south and tin along the river that divides it from Portugal. And I remember learning that most early civilizations emerged around fertile river valleys, which seems to exist as well. So why did a bronze age empire not form in Spain?
I'm guessing that at least one of my postulates is plain wrong. But which?
The incorrect postulate is that the Iberian peninsula did not feature Bronze Age civilizations. There were, in fact, several distinct cultures. Do some searching for El Argar / Argaric Culture fro the Early Bronze Age, and its continuation into the Middle Bronze, and its decline into the Late Bronze Age. Then look for the "motilla" ("little hill") settlements in the arid regions of La Mancha, whose material culture shares much with Bronze Age cultures elsewhere in Southern Europe. Also have a look at the Late Bronze developments in the Guadalquivir valley, and the Late Bronze "invasion" of the proto-Celtic "urnfield culture" in the NE of the peninsula. Finally, look for the interaction of western Iberian bronze age sites with other Atlantic LBA cultures in the British Isles and France (and possibly N. Africa), often called the "Atlantic Bronze complex" (this is more in the "Iron Age" of the cultures further East in Greece and the Near East, technically: ~1300-700 BCE).