Two weeks from now will mark the one-year anniversary of the war in Yemen – when nine countries led by Saudi Arabia began an aerial bombing campaign in Yemen. Many of the airstrikes over the past year appear to have been unlawful – including 36 attacks that I and my colleagues investigated that killed more than 500 civilians. Residential neighborhoods, markets, schools, and hospitals have all been bombed. Some attacks may have been war crimes. If you are diligent about reading the news, you may know this already.

A boy stands in a classroom at his school after it was hit by a Saudi-led air strike in Yemen's capital Sanaa July 20, 2015.

What you may not know is that because the United States has provided targeting assistance and other direct combat support to the Saudi-led coalition, it is a party to the conflict, which places important international legal obligations on the US.  What you also might not know is that US weapons have been used in unlawful airstrikes – and could perhaps in the future.  According to the US Congressional review, between May and September 2015, US companies sold $7.8 billion worth of weapons to the Saudis, some of which may end up in Yemen. In October, the US government approved another arms sale to Saudi Arabia for $11.25 billion, and just a month later Washington signed another Saudi deal, for more than 10,000 advanced air-to-surface munitions including laser-guided bombs, “bunker buster” bombs, and MK84 general purpose bombs, worth $1.29 billion. The Saudis have used all these weapon systems in Yemen.

Tonight, “Vice on HBO” is screening a documentary that captures the devastating human cost of this war. Every American should watch the documentary – to know about US involvement in a war that Washington never bothered to tell you about. It’s on at 11 p.m. Eastern Standard Time, and available to subscribers to HBO online.