Why was World War 1 more deadlier than ww2?

WW1 used trench warfare. Causing a dead zone. where if anyone popped out of their trench they would most likely died. It cause many stalemate conflicts. Also, planes, tanks, and gas (even gatling gun) were new styles of fighting brought out by this war. So no tatics were thought of during this time. Laslty, during this time there were many treaties of allies going on, causing many countries to join the war when it was only two tiny countries that were actually angry. Look up ww1 western front and eastern front to learn of trench warfare for this was primary cause of the many deaths.