What does allied victory in World War 1 had been brought so dear as to be indistinguishable from defeat mean?

Answer 1

it means that there were so many casualties that it didn't matter that they won because they lost a ton of money, people and there were even spiritual costs.

Answer 2

Winston Churchill, Great Britians prime minister in the 1940's and the 1950's

Answer 3

It means that even though the battle was won, it was so expensive in terms of men and material that the battle might as well have been lost. ( see Pyrrhus, and Pyrrhic victory.)