What technological advancement significantly changed warfare in World War I?

The introduction of trench warfare significantly transformed the nature of combat during World War I by leading to a protracted stalemate on the Western Front. Trench warfare involved the digging of extensive networks of trenches where soldiers would live, fight, and take cover from enemy fire. This method changed military strategies and tactics, as armies had to contend with new realities such as muddy, unsanitary conditions and the challenges of safely advancing against entrenched positions. While new technology, such as machine guns and artillery, made frontal assaults extremely deadly, trench warfare forced military leaders to rethink how battles were planned and executed, often leading to horrendous casualties without significant territorial gains.

The development of armored tanks, on the other hand, while an important advancement towards the latter part of the war, was initially limited in deployment and effectiveness. The atomic bomb was not developed until World War II, and air conditioning, while beneficial for command centers, did not impact warfare directly in the same way as the introduction of trench warfare.