The Twilight 2000 4e/Road to Armageddon games are built around a slide into WW3 and the aftermath, giving the GM the option of gaming at the days just before the war, the war, or the aftermath. Incredible detailed support.
Although you've confused the role of the government with the role of the economy in your first post.
And big corporations are a stabilizer, not a point of crisis.
Your need a catalyst agent for a collapse, however; systems do not just generally wind down, even at a national level. For example, the collapse of Royal France in the late 1700s was caused by a series of debilitating wars with Great Britain, the return of conscript military forces who had been exposed to the ideas of the American Revolution, and a savage economic downturn. And even then, France did not cease to exist. True, the rebels killed each other, and they entered into what amounted into a world war, culminating in service to an Emperor who was later deposed and replaced by a King, putting them, millions of deaths and mountains of spent treasure later, right back where they started.
Society is a tough beast. Complete collapses of a nation are extremely rare in history; a multi-national collapse has never occurred.
So you need a specific trigger: occult or alien invasion, limited nuclear exchange (a full exchange would sterilize the entire planet), unnatural disease the like of which Mankind has never seen, etc.
