Explanation: On the Western Front in WW1, unofficial truces were sometimes honored between the warring sides for holidays, especially religious holidays, though the brass tried to crack down on it (often successfully).
On the Eastern Front in WW1, unofficial truces were sometimes honored between the warring sides because fucking wolves developed a taste for human flesh from starvation from all the war scaring off their usual prey. These included officer-approved truces, because being attacked by wolves was something both sides agreed was a poor way to go in a shooting war.