In Ukraine, human rights investigators like Amnesty International and Bellingcat have been tracking Russian attacks to aid in a potential war crimes investigation. One thing they’re paying special attention to is cluster bombs. Cluster bombs were first used in World War II, and scatter numerous smaller bombs over a wide area — often killing civilians. It’s this indiscriminate nature that often makes their use a war crime.

Our modern conception of war crimes was established by a series of treaties whose creation spanned decades. In 1977, one of those treaties banned what’s known as “indiscriminate attacks.” That means militaries are legally prohibited from attacking an area imprecisely, in a way that can harm civilians.

Russia is not alone in using these weapons: In conflicts since the 1977 treaty, many militaries continue using them in civilian areas, with impunity, including the US. This video explains how they’re being used by Russia, and why places like the US and Russia just won’t give them up.

This video is part of our ongoing, broader coverage of the Russian invasion of Ukraine. For more videos that provide historical context to the headlines in the news today, watch our playlist here.

You can find this video, our playlist, and the entire library of Vox’s videos on our YouTube channel.