the second world war ----- million of people were killed end

主干划分The second world war ended
in which million of people were killed 做war的后置定语,译为在那场数以百万人丧生的二次世界大战,这里主要是war不是时间感念,因此不用when
可能弄成主要你更容易理解,"In" the second world war,millions people were killed.That war ended in 1945.