The world's oldest federation dates from 1789; the newest, from 2015
The United States constitution took effect on 4 March 1789, making America the oldest federation still standing. The newest is Nepal, whose constitution came into force on 20 September 2015. Between them, federations now house roughly two in every five people on Earth, from giant India to tiny Saint Kitts and Nevis.
A federation joins partly self-governing regions under a central government, and the key feature is entrenchment: neither level can rewrite the division of powers without going through constitutional amendment. That distinguishes it from a unitary state like France or Japan, where regional autonomy is delegated by the centre and can in principle be withdrawn. Member states usually have no foreign policy of their own, though Germany's Länder hold some such powers.
Paths to federation vary. The United States and Switzerland grew from agreements among separate states seeking common defence. Australia is unusual in having been created by citizens of each colony voting yes in referendums to adopt its constitution, and like Canada it federated while still inside the British Empire. India, Pakistan, Nigeria and Malaya became federations around independence. Austria, a unitary empire of crown lands, became a federation of Länder under its 1920 constitution after the Habsburg monarchy dissolved.
Not every experiment lasted. The Federal Republic of Central America broke apart in under twenty years, Argentina swung between federal, confederal and unitary arrangements before settling, and Brazil only federated after its monarchy fell. Germany has moved between confederation, federation and extreme centralisation. The Soviet Union, founded in 1922, was formally a federation of republics but in practice tightly controlled from Moscow, a pattern the Russian Federation inherited. More recently, Bosnia and Herzegovina, Iraq since 2005 and Somalia since 2012 adopted federal structures to manage ethnic conflict.
Some federations are asymmetric. In Malaysia, Sabah and Sarawak joined on different terms from the peninsular states and retain more autonomy. Constitutions may also give the centre emergency powers: India can impose President's Rule when a state government breaks down, and Canada's Parliament can legislate for peace, order and good government. Many federations are large and multi-ethnic, yet size alone does not dictate the choice, as Micronesia's federated states show.
Source: Federation
