The United States stands at the center of a far flung global alliance system, which commits it to defend the security of countries rich and poor, great and small, liberal and illiberal. The principal U.S. formal alliances are the North Atlantic Treaty Organization, the U.S.-Japan security treaty, the Republic of Korea Treaty, and the Australia-New Zealand (ANZUS) treaty. The United States has less formal relationships with Israel and several Arab states, and many others around the world. The foreign-policy establishment insists that all of these alliances are central to our security. The reasons offered since the end of the Cold War to support this judgment are seldom clear, and the costs are always buried, if acknowledged at all.