The Imperial Federation was a proposal in the late 19th and early 20th centuries to create a federal union in place of the existing British Empire. The project was championed by Unionists such as Joseph Chamberlain as an alternative to William Gladstone's proposals for home rule.
At the time, the British Empire consisted of many colonies, some of which were largely self-governing dominions (Canada, Newfoundland, Australia, New Zealand, South Africa) and others were not (India, West Indies, Fiji). The future of the empire remained uncertain, as it was unclear what the end result would be if all colonies eventually became self-governing. Among other concerns, it would be very difficult for British interests to be maintained if every colony was essentially already sovereign.
Creating an Imperial Federation thus became a popular alternative proposal to colonial imperialism. The plan was never firm, but the general proposal was to create a single federal state among all colonies of the British Empire. The federation would have a common parliament and would be governed as a superstate. Thus, Imperial unity could be maintained while still allowing for democratic government. The colonies would increase their influence while Britain would be able to share the costs of imperial defence. The best features of large states could be combined with the best features of small states.