Federal and confederal were once synonyms meaning a simple treaty league
Both words grow from the Latin foedus, a treaty or covenant, and until the late eighteenth century both described a league of sovereign states. James Madison called the new American constitution a blend of national and federal, and during the nineteenth century federalism came to name that hybrid instead.
Federalism divides governing power between a central government and regional units such as states, provinces or cantons, neither simply subordinate to the other. In a confederation the centre depends on the member states; in a unitary state such as the United Kingdom the regions depend on the centre, even after devolution. Federations today include Argentina, Australia, Brazil, Germany, India, Nigeria and Switzerland, and some describe the European Union as one. Several are democratic in name only, Russia being cited as an example.
Its roots go back to alliances of tribes and cities. Historians often begin with the Israelite tribal confederacy led by figures called judges, around 1200 to 1000 BCE, and continue through Greek leagues such as the Aetolian and Achaean. Johannes Althusius, who died in 1638, is regarded as the father of modern federal thought, alongside Montesquieu, whose 1748 treatise surveyed villages combining into a polis and cities forming confederations. The Old Swiss Confederacy practised it from the mid-fourteenth century.
Countries reach it by two routes. Integrative federalisation turns a confederation into a federation or folds new populations into one, while devolutive federalisation converts a unitary state into a federal one. Daniel Ziblatt identifies four explanations for why states adopt the model: strong decentralist ideals, ethnically or culturally divided populations, a bargain between a centre too weak to dominate and a region too weak to secede, and regional units that already possess modern administrative machinery.
Supporters argue that divided power guards against tyranny and lets a country be both large and diverse. Immanuel Kant claimed that even a nation of devils could build a working state if its constitution set rival factions against each other within binding checks and balances. Political scientists sometimes use federalism more broadly still, for any layered, pluralistic arrangement of social and political life.
Source: Federalism
