Just to be clear, all you are going to find are hypotheses. As many have said here, no one knows quite for sure.

In broad strokes, it was systems collapse based on trade of rare resources. The Mediterranean economy at the time was based primarily on copper and tin, which made Bronze (thus the name of the age). Tin, however, is rare, so it's a weak point in the system. Disrupt tin and the whole system breaks down.

But how exactly did this get disrupted? Was it ecological? changing climate? Raiders from outside the area? Most say it was all of that and more. Someone cites that they do see evidence of a string of volcanic eruptions during this time period, which could have led to drastic and sudden environmental change and this could have changed things such that food was scarce and people turned to invasion and war to find resources and feed themselves. But this is a string of hypotheses tied together with no evidence other than a couple of tablets referencing sea peoples.

What's great about this period however it's a bonafide actual mystery puzzle that tantalizes the imagination with something real, and not those BS "ancient aliens" documentaries on the history channel. You have to be ready to accept that you are not going to find definitive answers but it will fascinate you.