One well-supported theory suggests a military innovation that enabled a cheaply-outfitted, quickly recruited army of 10,000 to defeat a standing force of 1000 charioteers. Such an army might be easily filled out from among the overtaxed farmers surrounding each walled city. In this alternative, the "dark age" might rather indicate freedom from centralized oppression, with "civilization" arising again only after its faults were forgotten; and the Catastrophe an early sort of "Mediterranean Spring".
There was never more than conjecture supporting the "Sea Peoples" idea. For the popular-uprising approach, we may imagine a core of a few hundred organizers proceeding from one city to the next, with local recruiting promises (and testimonials from the last) of rich spoils from each new target.