Why was World War 2 bloodier than World War I?

World War 1 lasted from 1914 to 1918 and about 8.5 million people were killed and another 21 million wounded more were soldiers than civilian

World War 2 lasted from 1939 to 1945 and over 70 million people died and of those 70 million, more were civilians than soldiers. Nazi murdered civilians, kids, women, old and sick people. No mercy. They maintained concentration camps throughout the territories it controlled.

More sophisticated weapons and technologies were involved, more countries and territories involved.

In 1941 German forces have invaded the Soviet Union and the war in Russia lasted until 1945 with about 30 millions dead just for Soviet Union.