For those of you who don't know what the Imperial Federation is, read this.
The Imperial Federation was a proposal to turn the British Empire into a federated superstate, which would combine the benefits of a large power with that of small, efficient governing. Member of this Federation would likely have been the largely British-descended dominions of Canada, Australia, New Zealand, as well as Ireland and South Africa.
"Supporters of Imperial Federation regarded the United Kingdom as having two possible futures; imperial union and continued long-term importance or imperial dissolution and the reduction of the status of the UK to a second-class nation."
Looking back now, we know that the British Government chose the latter choice. But, should the first choice have been taken? With an Imperial Federation, Britain might have maintained its status as a big international power, instead of the decline we witnessed in the 20th century.
Using contemporary statistics, the Imperial Federation consisting of the UK, Canada, Australia, New Zealand and Ireland would have had:
A population of roughly 125 million
An economy with a nominal value of 5.381 trillion dollars, which would have made it the second largest in the World
Would have spanned three continents