Explanation: A federation can be formed in two ways, that is, by way of integration or by way of disintegration.

• In the first case, a number of militarily weak or economically backward states (independent) come together to form a big and a strong union, as for example, the US.
• In the second case, a big unitary state is converted into a federation by granting autonomy to the provinces to promote regional interest (for example, Canada).
• The US is the first and the oldest federation in the world. It was formed in 1787 following the American Revolution (1775–83).
• It comprises 50 states (originally 13 states) and is taken as the model of federation.
• The Canadian Federation, comprising 10 provinces (originally 4 provinces) is also quite old–formed in 1867.
• The Constitution of India provides for a federal system of government in the country.
• The framers adopted the federal system due to two main reasons–the large size of the country and its socio-cultural diversity.
• They realized that the federal system not only ensures the efficient governance of the country but also reconciles national unity with regional autonomy.

Source: Laxmikanth Polity