The world has grown far too familiar with genocide; as mass killings have claimed countless lives, the word has become ingrained into our vocabularies. But the term didn't exist until 1943, when Polish lawyer Raphael Lemkin coined it — pairing the Greek "genos," meaning race or family, with the Latin "-cidere," for killing. Lemkin, who witnessed the massacres of the early 20th century, spent his life campaigning to make the world acknowledge and prosecute the crime. A new documentary, Watchers of the Sky, tells his story. Once he'd established the word, Lemkin worked persistently in the then-newly-formed United Nations, hounding delegates to discuss his new word and acknowledge the issue.