There was a similar event last year in the Netherlands, called Project X Haren (Google Translate link).
A girl left an invitation open on Facebook. 250.000 people invited each other, and 30.000 people said they'd come. Eventually the visitors, mostly soccer hooligans, destroyed everything in the small town's center, and special forces had to control the visitors. If you'd look at the imagery on the news and on the web — it looked awful, almost, but not quite like a war.
I seriously can't comprehend people like that.