There is no uniformity in the way in which the federal States are created. It depends on the historical conditions, the purpose and aims of the federation and the geography of the federating States, to determine in what way of a federation would come into being. Broadly speaking, the federal1 unions are the result of two opposite forces, the centripetal and centrifugal tendencies of the federating States. In other words, a federation is either a result of integration or of decentralisation.
In the case of integration, a number of sovereign States voluntarily decide to unite together into a single federal State in view of a common foreign danger of aggression and for common defence or of some economic advantage resulting from union. Such a union is a result of centripetal forces. The federations of the U.S.A., Switzerland and Australia came into existence in this way. The second method of creating a federal State is the decentralisation of the existing unitary State. Such a State is usually too large to be administered conveniently from a single governmental centre.
It has also a great diversity of language, culture and local interests which could be satisfactorily looked after by the autonomous local governments. These are the centrifugal forces which require that the former unitary State should be transformed into a federal union. The federations of Bharat, Pakistan and the Soviet Union came into being in this way.