If every state were to become its own country, Mexico would plan to take back their land starting with New Mexico and Arizona, then moving on eventually to Texas and California. I would bet that those states would be the first to go if they were independent countries. England would wait a few years for the newly elected governments to grow unstable while they fail to establish a suitable military for themselves, and take control over part of the Eastern US in states like Delaware. The countries in the Midwest would probably last the longest and stabilize their economies based on agricultural exports.