Inhumanity is very cruel behaviour — the noun for that cruelty. It can name the quality (there was so much inhumanity) or the cruel acts themselves. Writers still say man's inhumanity to man: people being terrible to people. It is a heavy, serious word, more at home in news, history, and speeches than in everyday talk. Though actually, it is not only about blood and war. Turning away when someone needs help, or running a system that slowly crushes people, can also be called inhumanity. One quiet fact: this noun is built from inhuman, not from inhumane, even though those two adjectives sit side by side in modern English.