cause-poison gas was introduced to the war -effect-people got killed and burned from gasses in trenches.

cause-they started making tanks -effect- it started to eliminate trench warfare

cause-flamethrowers were made by germans -effect- the enemy was scared out of the trenches and trench warfare started to decline.

cause-machine guns replaced rifles-effect- they could shoot at the enemys at a faster rate and could eliminate the enemy easier.

cause-zeppelins were used by germans-effect- some british cities were destroyed.

cause- submarines were used by the germans-effect- british supplies ships were being destroyed and britain couldn't get any supplies.