The British Empire alone, still had a huge demographic advantage over the Axis nations it was formally at war with, if Whitehall choose to include the colored populations of the Far East, Africa and the West indies, along with the French-speaking Canadians.
By and large it did not.
If the army forces placed in Britain as a potential invasion force against Germany's home territory had to be too small to do the job as a price for remaining basically all-white and all Protestant, so be it.
Because if Britain's infantry was boosted by six million Indian "colored" volunteers that then led the successful invasion into Germany (at the cost of the de facto recognition of the postwar independence of India) then Churchill and ninety percent of the English elite wanted no part in it.
The lessons of The Great War for the world's elites : modern all-out war unleashed social changes almost worse than abject military defeat...
Over and over, all the Allied nations (along with the Axis, by the by) chose to be at a military disadvantage, in a total war situation, rather than risk the unleashing of the social consequences of a Big Tent coalition, because it would result in a too wide a sharing of the moral success of victory.
One almost feels that if the elites had believed that the war could have been successfully conducted a small elite force of middle class volunteers in metal machines of submarines, airplanes and tanks, waging war from far above the fray, they would have done so.
Foregoing the conscripting of mass infantry armies of working class men, all demanding postwar pensions and political and moral rights that come from having personally defeated the enemy in old fashioned face to face combat.
It was the united effort to avoid sharing the wartime responsibilities, if it also meant sharing postwar power, that Dr Henry Dawson set out to combat with his personal Manhattan Project ....
* Who can forget Stalin's northern naval base that he provided for Nazi u-boats - who besides the apologist historians for the Allied cause ?