Frankly I didnt think the USSR activity during that period deserved a mention because during the period between August  MolotovRibbentrop pact and June  Barbarossa it was not a major player How do you propose to fix it Frankly the situation is very complex because from  Sept  to  June  the USSR  Won a border war against Japan  Expanded its territory at the expense of some Central European states  Conducted a war against Finland  Negotiated about further division of the spheres of influence with Germany  Remained formally neutral How all of that can be described in few words Probably  apart from formally neutral USSR which also expanded its territory at the expense of some of its neighbours From one hand if you think it would be not too wordy for the lede we can add that From the other hand I am not sure it would be absolutely correct in a situation when conquest of Norway Danmark Greece or Yugoslavia is left beyond the scope totally