In every modern political system, power is shared to a greater or lesser extent between levels of government. These power sharing arrangements are perhaps most explicit in formal federal systems like the United States and Canada, where federal constitutions define the relative powers of central and subnational governments. They may be no less important, however, in unitary democracies and even authoritarian regimes where central governments require local actors to implement policy on the ground and often delegate significant authority to them. Indeed, in any large and complex modern society, effective governance requires some sharing of power between higher levels of government, capable of coordinating many disparate actors and interests, and lower levels of government, capable of responding to local conditions.