Which sea peoples' invasion helped end the Bronze Age around 1200 BC?

The Sea Peoples, and nobody knows who they were. The name comes from Egyptian inscriptions listing groups - Peleset, Shekelesh, Denyen and others - who attacked by sea and land, and the identification of those names with known peoples is guesswork that has been revised repeatedly.

What happened is not in doubt. Within about fifty years around 1200 BC, the Hittite empire vanished, Mycenaean Greece collapsed, cities across the Levant burned, and Egypt survived in a much reduced state. Writing systems were lost - Greece entered several centuries with no literacy at all - and trade networks that had moved tin across a continent stopped.

The single-cause explanation has been steadily abandoned. Current accounts describe a systems collapse: drought evidenced in pollen and isotope records, earthquake sequences, famine, and an interdependent trade network in which bronze required tin from thousands of kilometres away - so a disruption anywhere propagated everywhere. The Sea Peoples may have been a symptom, displaced populations moving because their own homes had failed, rather than the cause. It remains the standard case study for how a connected world can come apart.