They shot at them, used barbed Wires and lines.
Basically, to shelter troops from enemy attack.
Chlorine gas was used to drive enemy men out of their trenches in order to make it easier to take the enemy trenches. Even now, it is used to soften up enemy positions.
Because In WW1 soldiers were running across trenches and getting constantly getting killed in mass numbers by Machine guns so engineers devices a way to keep soldiers alive, and stop the enemy and destroy their trenches.
Because it was a good way to get close to the enemy without getting your head blown of. They were also a good way to stop the enemy. the big problem was the same rules aplied to both sides.
The trenches were dug in lots of countries. France,England and Germany were included. In fact, most countries in WW1 had trenches dug in them either by them or the enemy.
It was used as a weapon during WW1. The gas was packed into artillery shells and shot into the enemy trenches.
To overrun enemy trenches without the enormous losses which had categorised the fighting in WW1.
They used shovels and picks to dig out the trenches.
it was to stop any enemy soldiers for advancing through the trench system.
There were electric light in German trenches in WW1 because they were more advanced and had better trenches than the British.
To smash thru the enemy's trenches (in WW1), without being stopped by machineguns (a bullet proof infantryman).
During WW1, soldiers were promised mostly money or a promotion for the capture, killing of enemy troops, or for capturing enemy trenches.