Which weapon of World War 1 contributed most to the stalemate or death on the western front during world war 1?

Weapons such as the machine gun and artillery made it very hard to cross no-mans land, or an open expanse between the two sides, and survive. Various gas weapons were also used to hinder infantry, such as chlorine gas and mustard gas. These gases would damage or kill foot soldiers. Some obstacles such as barbed wire, mines, and terrain also made it difficult to attack.

With the introduction of tanks, it was much easier for armies to break stalemates and advance into enemy territory.