Between the Holodomor, the Kulak Operation, the Polish Operation of the NKVD 1937 - 1938, Vinnytsia Massacre, the Great Purges, the National Operations, Kharbin Operation of the NKVD, German Operation of the NKVD,
mass killing's by the Gulag system / Mass deportations,etc. etc.
What was the USA supposed to do at the time? We were not the biggest military in the world at that time. We were a young nation thousands of miles away. Also ask your self why hitler and napoleon failed invading russia. The west could do nothing to stop it! That is why they did nothing!
PS. We had our own problems at the time!
The U.S.A got involved late in WW2, but on the Soviet side!
Not that I'm pro-Nazi, because I'm also anti-Nazi.
But, as for Britain, and France, they didn't declare war on also Soviets for also invading Poland, and then went onto appease them.
Ultimately when a 1930's genocide akin to the size of the Holocaust went on, the World did nothing.
Personally, I think Britain especially, and to a lesser extent France were setting up Poland, and Germany to get steam-rolled by Soviets.
I think the agenda of WW2 for Britain, and France wasn't so much about helping Poland, as more about stopping the Nazi ideals, and considering they did nothing during the 1930's Soviet regime, it seems it's not so much about genocide being a problem, as it was about stopping the Nazi idealogy.