Why was World War One been described s a total war

Total War is when the entire resources and population are mobilized towards the war effort, which takes priority over everything else. Further, Total War also involves prosecuting the war against the entire population of the enemy, not just against its military.

Answers:

Conscription into the military for all countries involved.

Women working in munitions factories, heavy industry, and many other jobs they hadn't done before. In Britain, women were conscripted into such work.

A War Economy adopted in Britain, France, and Germany, whereby manufacture of weapons, munitions, and other war materiel was prioritized.