There are three main types of governments based on who rules and citizen participation: autocracy, where one person holds power; oligarchy, where a small group holds power; and democracy, where citizens hold power. There are also three systems of distributing power: unitary systems have all power centralized; confederations have a weak central government and strong state/provincial governments; and federal systems share power between central and state/provincial governments. The UK has a constitutional monarchy, parliamentary democracy, and unitary system, while the US has a presidential democracy and federal system.