Why do people "on both sides rush to join the fight"? (In WW1)

Answer: The young men went to war with the song.

Explanation:

Across Europe, young people were delighted to welcome the war. They enlisted en masse to go to battlefields. National armies numbered an estimated number of soldiers.

The reason for this is the fear of these young people that if they do not make up for the military, they will miss a fascinating period of their lives. So they sang enthusiastically, boarding trains that shipped them to the front lines, unaware that we were slaughtered.