I think one issue you may be having with your research is that the "Bronze Age" will be at a different time depending on where in the world you are looking. Each region has its own archaeological periods. for example, while the Levantine (eastern Mediterranean) Bronze Age extends from around 3000 BC to around 1200 BC, the Bronze Age in central Europe extends all the way from 3000 BC to around 700 BC. In Europe, while a period of time is usually considered to be the "bronze age", it is usually referred to by "cultures", or identifiable groupings of material culture which occur for a period of time, such as the Lusatian culture and Halstatt culture in central Europe. It's just a slight difference in the way archaeology is conducted in Europe due to the differences in material culture. The Near East has a lot of textual evidence and inscriptions, because of the comparatively early onset of writing, which allows us to identify people groups and their relationships with other cultures of the time. In Bronze Age Europe, we don't have that luxury, and cannot determine what ancient people groups defined themselves as or called themselves or how they distinguished themselves from other groups, so we have to build those distinctions ourselves. We do this by assembling a material culture set, which involves examining all the artifacts from the region and noting changes over time and space. We can divide these into blocks which are "cultures". These cultures may or may not correspond to what we might think of as "polities", or political entities. One culture might be a single large tribe or kingdom, or it might be a bunch of semi-nomadic tribes who are politically separate and independent yet share the same material culture and technology. Without writing, the two are not easily distinguishable. So in Europe, we divide up the periods based on what appears to be the dominant material culture set in the region.

In the Levant, it's quite different. We have writing, so we can tell the political organization of the various groups. For example, the Amarna Letters from the end of the Late Bronze Age tell us about how Egypt is administering its vassal states in Canaan, which are all organized in a city-state system, and which have a certain amount of autonomy and which often have disagreements with each other. We can also see the beginning of the end of the Late Bronze age in these letters, as they tell about the coming of the Sea People, as well as the incursions of the 'Apiru, the land-based version of the Sea People coming from the east. Because we can see the political organizations, it is easier to divide things up and we don't need such huge chunks. So we can combine a number of these smaller divisions into larger epochs, divided by major change-inducing events which we often know something about based on the textual evidence of the time. We know a major change occurred around 1200 BC, because we can see it in the texts, we can see it in the artifacts. So we make that a major transition point.

To be honest, Bronze and Iron Ages in the Near East are much less about how common each of those metals are, as about dividing up time based on major events, and those were some handy terms which also happened to coincide with the dates for these divisions. Bronze is still incredibly common in the Iron Age (can't say I personally have excavated much that was iron from the Iron Age, while I have excavated a lot of bronze objects from the Iron Age, but that may be due to preservation conditions).

Most of the discussion on the Collapse is centered around the Eastern Mediterranean, because that is the most notable situation at this time. Because the Bronze Age ends at different times in other places, it is most likely not part of this same series of events that led to what is known as the Bronze Age Collapse.

A number of situations occurred at the same time which helped the Collapse along. Most scholars believe that environmental factors played a part. The Bronze Age was much wetter than the succeeding Iron Age for the Near East, according to studies like this one, and the relatively sudden aridity probably caused a certain amount of famine, meaning many economies were severely impacted, which probably contributed to the downfall of many societies. The influx of raiders, both on sea and on land also contributed (the Sea Peoples and the 'Apiru). Egypt's power basically broken when Rameses III fended off the Sea People's invasion of Egypt, which meant that most of the Levant which had been under Egyptian sovereignty then was left to its own devices, while Egypt focused on itself, recovering from the combination of famine and massive military losses.

I can't tell you about the end of the Bronze Age in China or in Europe, but I know that Europe at least happened at a different time, so it would have been a different series of events leading to that transition. Most of the events leading to the Levantine Bronze Age transition were specific to that area of the world, a combination of military, climatic, and political/social changes.

Keep in mind that not all places suffered a "collapse" in the Eastern Mediterranean. In fact, Cyprus fared fairly well while its neighbors succumbed to the pressures of these foreign people. That isn't to say that Cyprus was unscathed by the collapse, several eastern Cypriot cities were attacked and destroyed, but its island nature and distance from the mainland did insulate it from the worst of it. There is a fairly solid continuity from before the start of the collapse to after the collapse within the archaeological record.

I find it interesting in Cypriot history that the beginning of the Iron Age is marked by the formation of 10 kingdoms on the island. One of these kingdoms was native Cypriot, one was Phoenician, and the other 8 were founded by Greeks coming back from the Trojan Wars.

1982 Sir David Hunt Footprints in Cyprus