Romania´s cause for war in WW2

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I am thinking that in the rules of what counted as a valid casus belli, I think Romania would have one against the Soviet Union, given the invasion and annexation of Moldavia by Stalin and threatened, in the same way, Finland was in 1939 and most people today see Finland´s war in that year as legitimate. Not a license to do war crimes of course, and not really a good reason to go all the way across the Ukrainian SSR and over to Stalingrad, or to annex a big part of Ukraine too in addition to Moldavia, but a casus belli that even in the eyes of the British and Americans (Stalin obviously is biased in this question), would be seen as legitimate. Did this affect the way that the Allies, the Western ones at least, treated Romania after the war or during it? Is my premise wrong to begin with like the debates over whether Mannerheim had a casus belli in 1941?