Usually said with a shrug of the shoulders, upturned palms, and a slight shake of the head "C'est la guerre" is a nicely ironic phrase used as an excuse for anything which goes wrong, often due to incompetence (sometimes one's own) or cirmumstances beyond ones control. A less elegant phrase would be "Hey, what can you do?"
Q "Tsk. Why do these trains never run on time?"
A "C'est la guerre"