Daft ideas: United Countries of Earth

The US provides the blueprint for a world with a federal* government. Nations would be like the various states in the union. They would be self-governing to a great degree; there would be religious tolerance, freedom, equality and so on. Any dictators, despots, tyrants would be removed before they became a threat. This goes beyond the United Nations. What if some countries took it into their heads to secede from the World Union? Then a terrible conflict on the scale of a world war might ensue.

*Federal: Of, relating to, or being a form of government in which a union of states recognizes the sovereignty of a central authority while retaining certain residual powers of government.