I know that the USSR wanted all of its republics to be seated, and the US vetoed and counter-requested that all of its states be seated. Why did Ukraine and Belarus get seats instead of any other republics (like Russia), and why did the Americans not pursue the same thing?
Our history textbooks say that happened because of severe casualties Belarus and Ukraine took during nazi occupation. Also some historians bring up a fact that there was a huge guirella warfare movement in Belarus from the very beginning of that occupation. This movement made a huge impact on eastern front and ensured the success of upcoming war effort.