The war of 1861 started over taxes. Ft Sumter was the taxing authority for the port of Charleston. It's guns and ships enforced the tax laws on imports and exports to the United States. When the South succeeded, the fort refused to go along giving Lincoln a cause to go to war.
Today, economics holds us together: the redistribution of wealth from one state to another. Can a state survive without federal tax dollars? Well yes, we simply hold on to the tax flow going to Washington DC and use it for ourselves. That would enrich some states and others would suffer a slight loss. Unscrambling the mess would be the biggest problem. Moving to block grants would be a good intermediate step and allow us to get the systems in place.