World War I started in 1914 and ended in 1918. While fighting, soldiers needed self-defense. So, they dug holes. The holes were two meters deep. These holes were called trenches. Most soldiers fought in the trenches. The trenches were not very far apart. For example, they could have been as short as thirty meters in between each trench. This open space was called No Man’s Land. Death was frequent, even when there was no fighting (for example, by diseases). This was called trench warfare.