A great question!
It may be helpful in answering to divide "Communism" into two parts: economic and civil systems of Russia under Stalin.
It may also be helpful to outline what kind of Communism was in play in WW2, Stalinism.
It may also be helpful to outline the sacrifices that Russia made in this war in comparison to other allied countries. Of the 55 million dead that WW2 left in its wake, 2% of these were British or Dominion troops, around a similar proportion were USA's troops. Some 60% of all the deaths of the War were Russian, mostly civilian.
World War Two in the European theatre was essentially a war between Germany and Russia sayeth the statistician. 70% of all the casualties inflicted on, and prisoners-of-war taken from, and materiel destroyed or captured from the Werhmacht was done so by Russian troops.
The only other Communist country at this stage was Mongolia which, with the help of Russian troops, actually scored the first defeat in battle against Japanese forces in the mid-1930s. Other than that, she was of little consequence for the rest of the war and shall therefore be held outside the scope of this answer.
Also beyond the scope of this answer is the War in the Pacific Theatre. Stalin declined to declare war on Japan until the day the bomb was dropped on Hiroshima. So "Communism" can be let go from this arena as well.
Prior to leaping into Russian economic and civil policies and the effects they played in defeating Hitler between 1941-1945, it would behove the studious to consider how "Communism" altered the playing field so dramatically in WW1:
Upon Lenin's revolution in October 1917, the new state imprisoned (and later executed) Tsar Nicholas II and his family and made peace with Germany so that the Reds could focus on fighting the Whites in the ensuing Russian Civil War.
The Treaty of Brest-Livotsk ceded large territorial areas to Germany in order to exit the war early. This left only one front for Germany to fight on. It is still unclear why the government capitulated in the West (it did not surrender). It was certainly not out of fear instilled in the war-hardened German soldier by the encounter of fresh US troops that came into the fray after the October Revolution.
It will not serve the question to bring to it consideration of Stalin's role in the invasion of Poland in 1939 (and the reclamation of the territory lost in 1917 to Germany Stalin would've thought, and that lost in Versailles in 1919 thought Hitler); in a similar vein, consideration of the Treaty of Non-aggression he signed with Von Ribbentrop prior to the fall of Poland help to isolate the essential element of the question.
So "Communism" therefore, of both the Leninist and Stalinist strains, was already a player prior to Operation Barbarossa in the summer of 1941.
Stalin, some ten years prior to the German invasion of Russia, famously said something like: we have ten years to improve our means of production before an industrialised enemy destroys us. Here he spoke of moving Russia from an agrarian to an industrial base of production.
Had he not made this happen (with a helping hand from thuggery no doubt), it is unlikely in the extreme that Russia could have held up against Hitler's mighty Wermacht; definitely the land superpower of its time.
Had the factories of Russia not been working around the clock to churn out T-34s, no amount of lend-lease could have saved agrarian Russia from inevitable collapse from the highly industrialised powerhouse that Hitler had turned Germany into.
Here, Stalin's view of Russia's economic base of production has been, in this author's view, unfairly overlooked by many students of History.
As Stalin came to accept more and more lend-lease from the US, communist economic systems become to muddied to explore as an independent variable. So other than Stalin's shift to industrialisation, it cannot be considered any further.
It is Stalin's civil structures that are most noteworthy from here.
Stalinism was quite a harsh form of Communism, Churchill recalls his sense of loathing when Stalin confided in him, through a translator, that he had some ten million Ukrainians killed prior to the War when he encountered resistance in the collectivisation of their farms.
So in this way, he was on similar terms to Hitler. Neither man gave much thought to civil liberties. The individual must die anyway said Hitler, it is the society that survives him, that is what we must fight for.
The question demands what role Communism played in the War. As the economy of Stalin's Russia has been considered, this leaves us with an enticing point upon which to muse:
What if Churchill took over Russia for the duration of the War, what if JS Mill or Roosevelt took the reigns from Stalin from 1941-1945? The only condition they had to fulfil is that they had to keep to their ideals of neo liberalism when dealing with Russian troops and their families. Could they have stood against Hitler?
The answer is: not a hope in hell.
Though industrialised and rid of feudalism in the History books, the average Russian was still a peasant farmer. He did not really care if the Tsar or Stalin ruled, he could not read or write, he had little appreciation of world affairs. He would probably not be able to tell you what "Communism" was. He would likely have been illiterate and ignorant... and smelly.
All he cared about was keeping his wife and children safe and fed by keeping as much as he possibly could whilst depriving the Tsar/Stalin/whoever-should-come-next of as much as he possibly could. Did he want to fight the next conquerer?
No way in the world! If Churchill had told him that we shall fight them on the beaches, and on the landing grounds, on the hills... he would have tried to keep his bemusement to himself whilst thinking of how to escape through these hills the new boss was describing.
If Roosevelt had made a rousing speech to him telling him of a distant harbour (that he'd never heard of and couldn't place on a map) that had been the subject of unprovoked aggression and the ensuing state of war that his country faced, he would have probably thought thank god it is not my problem! I have never even seen a boat!
Nope. JS Mill would've called Stalin back. Then he would have written another book perhaps called On Totalitarianism. Mill was very wise indeed.
The only bloke that could've pulled Russia through that god-awful hell of Hitler's machination was Stalin.
Only through mass conscription at gunpoint would the Russian farmer go and fight.
Only through the threat of imprisoning his wife and children should he surrender to the Germans stop him from simply surrendering the first chance he had (in fact, Stalin had to imprison his own daughter-in-law and grandchildren when his son surrendered)
Only by pointing firearms at those in the front and threatening to shoot them should they retreat would the Russian peasant not simply run away.
Only through the threat of immediate execution by firing squad could he convince the peasant not to injure himself, not to disobey, not to sleep on picket, not to do all the things that would come naturally to the average citizen of WW2 era Russia.
It was only through the momentum gained after the defeat of Hitler's Sixth Army in Stalingrad at the end of 1942, victory upon victory against the Werhmacht from 1943 onwards, that the Russian peasant-conscipt became a Red Army Soldier.
It was only because Stalin had held that firearm to the peasant's forehead, only because of his threats made on his family in his stead, only because Stalin would be second only to Hitler in shooting him should he see him turn and run. This was the only way they could've made it to 1943 as History records.
And only in Stalinist Communist Russia can all these brutish contraptions be found. Even Hitler seemed positively girlish in his approach to Dictatorship when compared to Stalin during the height of the War.
So, the role that "communism" played in WW2 was essentially the defeat of Hitler in early May 1945 when Russians alone fought the final battle in Berlin at the cost of yet another 300,000 troops. The British, Free French and US troops were miles to the west, just as Roosevelt and Churchill had previously agreed with Stalin. The loss of such great numbers made them a little squeemish anyway, they had elections to win after all!
Also Stalin. He had reminded them (probably during the Yatla Conference) that it was his country that had lost the most to Germany (twice as much as China, the second biggest loser in the War) and had inflicted the most damage in return, it would be Russian troops that took Berlin without the aid of the western allies who were touring around Europe taking pictures with their new cameras from mid 1944.
Two years of facing Hitler alone before the western allies landed.. two years of facing Hitler's "Total War;" where women and children were targeted for execution on racial and religious grounds. Soldiers treated as untermenchen because they were Slavic instead of Caucasian.
Two-thirds of the "Big Three" could not fault his logic then, just as the this author cannot today.
Without Stalin, there would have been no Stalinism, without Stalinism, it is unlikely that the Allies would have fought their way to Berlin. It would have proved difficult to bomb with the invention of the ME 262, the first jet-fighters. Hitler would have smashed a ruler weaker than Stalin.
It was in attacking Stalin that Hitler finally found himself. He got to see a real dictator in action. I often wonder what his thoughts on Stalin were the hours leading up to the moment on the day of his wedding when he committed suicide. Could he see a part of himself had been unleashed on Germany?
Probably not, "Bolshevism" was high on Hitler's hate list. He had to attack it, despite the fact that it had more in common with him than he may have dreamed.
Alger Hiss
Mccarthy
Korea became a non-communist country after world war 2. adolf Hitler died .
I think Russia.
Ho Chi Minh.
There are several communists from World War 2. Albania is one of the communist nations that came after the Second World War China is also another communist nation.
Batista but he wasnt communist
Moscow
no
Joseph Stalin
East.
The World Socialist Movement.
A communist government
Communist.
tito
Stalin
Joseph Stalin