Are we really rich?

If the good old USA is the richest nation in the world, why are we borrowing so much money from foreign countries like England and China and others? What would happen if all these countries all decided they wanted all the money paid back on the same day?Makes one wonder what we are spending our money(or theirs)on and is it worth it? Should we really be so indebted to all these countries? Thinking of the current national debt,where are we going? If the USA had to run on a balanced budget like the average citizen what would happen. What would the credit score be?