In analyzing the current unipolar system, it is useful to begin with structure. No other state or plausible coalition can challenge the unipole's core security, but this does not mean that all its values are safe or that it can get everything that it wants. Contrary to what is often claimed, standard balance of power arguments do not imply that a coalition will form to challenge the unipole. Realism also indicates that rather than seeking to maintain the system, the unipole may seek further expansion. To understand the current system requires combining structural analysis with an appreciation of the particular characteristics of the current era, the United States, and its leaders. Doing so shows further incentives to change the system and highlights the role of nuclear proliferation in modifying existing arrangements.