It has happened once it can happen again. Look when the "mother of all financial crises" hits the world and we go into Great Depression II the country will fragment, you now it and I know it. I cannot envision a scenario where the USA does not fragment.
Easiest thing for a state like Texas to get back on its feet following a collapsed Depression scenario is to unhitch form the swamp thing on the Potomac.
In the event of a massive crisis, I could see the dissolution of many countries, including the US, as we know them. What I question is whether such a crisis will occur — strictly speaking, it should have a while ago. Those who hold the reins, so to speak, won’t let the horses run away with them, because they know that it wouldn’t help their end game. They’d much rather guide the US (and other countries) in a careful, gentle descent, letting people subconsciously acclimate to each new level of soft tyranny, until the population is cheerfully living in Hell on Earth and the 10 people left who refuse to have a microchip planted in their palm or forehead are “liquidated.”