This book examines sources of conflict and instability in the US. Especially since 2008 a predominant theme has been the role of opposed social cultures and values within America. However, the main causes of instability have become the institutional fragmentation of power. There are many ways in which policy initiatives can be blocked, delayed or weakened—by other levels of government or by separate institutions at the same level. Yet, only quite recently has the Constitution’s role, widely believed earlier to be a bulwark of American democracy, started to become a weakness for it. This book argues not that the US Constitution is in imminent danger, but that the possibility of major failure, or of inaction in some policy areas, has increased greatly. The world after 1945, in which the American polity predominated, is one of its reduced power, with some rivals now having greater opportunities to frustrate US initiatives. Increased internal divisions have been crucial to its effectiveness both internally and in international arenas.