re: If the entire world attacked the USA...

It would have to be a extremely long and sustained attack to do it, but the world could do it. They could slowly eliminate our resources and just hold us hostage while they strategically attacked our food and resources from Canada and Mexico. No need to invade when you can starve out the country. Just too much of the rest of the world for us to attempt to do the same if literally everyone was against us. Europe, China, and Russia could easily arm everyone enough to do it. Would just take a long time to eliminate our resources to where we couldn't replace them fast enough. Especially when we are very dependent on other countries for some resources.