It started in WW1 and gained Momentum in WW2. The Empire was all of the colonies spread out around the world, now after WW2 in Europe, these countries who fought there under their own flag, now wanted recognition as being an independent nation who could fight in war. Associated to but not ruled by Britain. They may carry on some of the traditions such as the money bearing the Queens head or their postage stamps have an image of the Queen, or they have a Governor General that is a representative of the crown and they may speak English...or their system of government is much like the British system...just because some things did not NEED to change. Weights and measures for the most part stayed Imperial units.
. Still, the colonies want to be recognized as an independent country.
This was no just in Britain, but France and Spain and Portugal lost territories, as well as the USSR, and Germany & Italy. While it all did not happen in one year ...it started....the desire to be "Recognized for their contribution to the war effort." they got independence.
Thank Churchill for that.