How does "Genocide" differ from "War"?

Genocide would be the targeting and killing of one ethnic race. Sanctions and closing of borders are set up to stop weapons,supplies and reinforcments from coming in. Using sanctions such as stoping food would not be considered genocide, It does seem confusing because in a war you are fighing a certain group of people, I guess it would have to fall under intention, think about world war 2 everyone was at war but the germans were the ones commiting genocide,because they were targeting and killing jews not for any political reasons just to eliminate them entirely.