Why were trenches so hard to assault in WW1?

Trenches were notoriously difficult to capture in the first World War, but this wasn't unique to the conflict. In fact, there was some use of trenches in the American Civil War which proved quite effective. But back to the question. read more

There were multiple reasons why trenches were so hard to assault and capture. In addition to the good answers given in other responses: There was not just one line of trenches. Rather, defenders had whole networks of trenches – a first trench, a second trench, a third trench, and so on, often interconnected. read more