I've heard it suggested that the best way to stimulate a bunch of startups is to collapse a big tech firm. I know of at least two clusters that can be traced back to big companies going under.
Or even half an industry. I don't think it's a coincidence a lot of significant technical developments or companies came out of the post dot-com "fallow" period of 2002-2006 (like the spread of Ajax, Rails, Django, .NET and Mono, Skype, WordPress, much of Web 2.0's innovation with Flickr, Twitter, and Facebook all founded in this period, AWS).
The Toronto-Waterloo tech corridor can be pretty heavily tied back to the slow implosion of RIM/BlackBerry over the course of the early 2010s. Even the companies that predate those events still benefited a lot from the glut of qualified personnel coming available, and there are others which had been funded or bootstrapped by early RIM employees.
Pretty sure that most of Silicon Valley, including Intel, was founded by people exiting Fairchild Semiconductor when things got rough there in the ‘70s.