The thing is an alliance would not last,you are forgetting Hitlers standards.Hitler designated Slavs at the lowest of the low for European races,and planned to have them executed and gassed like he did to the Jews once the war was finished.However,at one point,Ribbentrop did look for a formal alliance.Ultimately the USSR's demands were unacceptable to the reich and Stalin's Land was invaded soon after.This was only for security,though,and they would be dealt with eventually anyway.
Mussolini disagreed with the Anschluss as part of his New Roman Empire idea he needed Austria.But soon he discovered Germany had more in common with him than not,so any alliance with the Allies was cancelled.
Its 1939.World War II begins as France and the UK declare on Germany and the USSR declares on them.Italy joins too,though not much happens.Mussolini would try an offensive in Austria and be pushed back to Venice.Poland is crushed as the Soviets actually invade with Germany.In 1940 Hitler invades Norway as usual,and invades France as usual.By now the Vichys and Hitler push Mussolini back to Rome,and he flees Italy.By 1941 the Axis control Rome.Meanwhile,Churchill is uneasy.Even an alliance with the USA looks like it will be pointless.Then Pearl Harbour.
Japan would not be abandoned by Germany,and it would have done its thing as usual,and even if he did,Hitler had no business declaring on Japan.Yamamoto still would have decided on Pearl Harbour,as I think the oil embargo still would've happened.Germany sent almost no aid to Japan in the normal timeline,so why would Stalin have done that in this timeline?
Its 1942.Japan loses the Battle of Midway,and Kokoda changes in Australia's favour.Relationships between Hitler and the USSR begin to get rocky as Hitler refuses to change his ideology for Stalin and racial tensions begin to spark in the Balkans and Poland.The UK loses the Battle of Britain,but as Stalin refuses to support an invasion of England,there is still hope.The RAAF rebuilds as the Luftwaffe stops bombing bases and starts bombing cities.Operation Barbarossa is planned,but Ribbentrop and Hitler do not agree with this idea yet.In 1943 The RAAF surrounds most of the Luftwaffe over London and the Luftwaffe and London are both wiped out.
Its 1944.Stalin withdraws all aid to Germany but refuses to invade Germany.The Manhattan project is nearing its final stages,and Japan is beginning to get desperate.Partisans in Yugoslavia continue to disrupt Germany,and De Gaulle and Mussolini call for landings in their respective regions.However Churchill thinks it is highly ambitious,and refuses.
In 1945 Japan surrenders slightly after VJ day in our timeline.Allied forces land in Italy,and begin pushing north.Nuclear bombs are landed in Hiroshima,Nagasaki and Munich.Hitler begins to get scared.Stalin formally makes peace with the Allies but doesnt invade Germany,and Germany doesnt invade it.
Its 1946.Landings in Normandy and Occitanie both liberate France.Mussolini is restored and Allied forces push into Austria.Partisans declare the Communist Republic of Yugoslavia and Germany no longer has any control over the Balkans.Landings in Norway cut off supply lines for Iron.In late 1946,Hitler commits suicide and Germany surrenders.Poland is given Danzig and Konigsberg but not all of the territory it does in our timeline.Italy allies with the USSR in a new cold war.Seven nukes are launched;Nagasaki,Hiroshima,Munich,Hanover,and Cologne.