uneeq:
1. Secession requires at most a 2/3 vote in the Senate to ratify a treaty, and probably only a majority vote in both houses of Congress. At worse, it requires a constitutional amendment.
2. Certainly states such as New York (and most of the states with large Jewish populations) would be bankrupt almost immediately, and would enter a full fledged depression, similar to Greece, often combined with hyperinflation.
3. The withdrawal of the United States from world affairs, as no state would have the capacity of raising sufficient military force to project power abroad, would probably be no worse than it was before the US started interfering in other country’s affairs (we remember the 1930’s, they were a good time, weren’t they?).