This French phrase of resignation gained widespread use during World War II. It provided the universal excuse for everything that was broken, no longer functioned, was unavailable or could not be accomplished. It also explained away all unusual behavior. That it is in the language of a nation whose life and joie de vivre was being crushed by an occupational army gives it an aroused sensibility.
The phrase lingered into European reconstruction and then into modern times in all nations. It is spoken with a wry acknowledgement of its former literal meaning even though it may currently describe any other interfering force preventing accomplishment of a task, even laziness.
Pierre: "No, no, she's a good girl. C'est la guerre!"
Howard: "Traffic has become so tied up every day that I have to allow an additional hour to get to the city."
Jimmy: "That's life in the big city, C'est la guerre."