Step-by-step explanation:
Trench Warfare was a deadly style of battle used in WW1. Both sides would dig in trenches, in order to overthrow the other trench, commanders would send out their men into something known as "No Man's Land". This was the ground between both trenches. The Defending side was fire artillery and machine guns to the attackers, this killed many soldiers and caused many casualties, for only a few kilometers land.
Answer:
Trench Warfare caused stalemates due to the many casualties it would take, and due to loss of soldiers. No side wanted to lose more men or risk deadlier casualties.