If I were to craft an alternate history scenario with the aim of having a shooting war between the Western Allies and the Soviet Union shortly after WWII...
1. Let's first suppose that George Patton wasn't killed in
August December 1945 and was able to continue to press for direct action to liberate Eastern Europe.
2. Harry Truman was President, and
the Truman Doctrine was the early U.S. version of 'containment' of the Soviet sphere of influence that more or less started the Cold War and led to stuff like 'Domino Theory' (which in turn contributed to the U.S. getting involved in Vietnam years later, among other things). Perhaps Truman could be pushed into a more aggressive posture, somehow.
3.
The Turkish Straits Crisis of 1946 was the first direct, post-WWII confrontation between the Soviet Union and the countries that would become NATO. Historically, a lot of U.S. wars have begun with some kind of naval action, an attack on an American ship or something along those lines. The actual Turkish Straits Crisis involved Turkish and Russian ships, but perhaps in our alternate history, we can postulate that a U.S. Navy ship gets directly involved, and damaged or sunk. Also, I don't know if the Turkish Straits Crisis is what prompted the US to post missiles and bombers in Turkey, which is what led to the Cuban Missile Crisis, or if Turkey was just a big, potential flashpoint during the Cold War and this was just another moment that it could have boiled over. Either way, maybe there's a thread we could pull on there.
4. I think the Poles in exile in the UK were agitating for the Western Allies to push the Soviets back to pre-war borders. I don't think they were ever close to getting what they wanted, but perhaps they could be part of a confluence of factors that pushes the US and UK back into war.
5. I believe there were also Germans - Wehrmacht - who were ready to join the Western Allies to liberate Berlin from the Soviets. I don't know how many there were, how serious they were, how well-armed they were, or who would have led them. But there was one moment, at the end of the war, when some Wehrmacht soldiers actually did join forces with a US Army unit, at
the Battle for Castle Itter. It was a small action that didn't play a big role subsequently, but perhaps that could be another log we can throw onto the alternate-history fire.
6. There were also something like 400,000 German POWs held in the United States by the end of the war (Wikipedia says 425,000). I think a lot of them liked the U.S. and generally got along with Americans pretty well. While they were in the POW camps, the German officers and NCOs maintained their military hierarchy and kept discipline. In some places, German POWs were allowed off the grounds of the prison-camps and interacted with civilians. Even if only half of them would have been fit enough to put their uniforms back on, that's, like, 15 or 20 divisions, well-rested and with some training and organization.
All in all, I think 1945 might be too soon. But with all of the above, I think you could get a conflict between the Western Allies and the Soviets in '46 or '47. This would be before the Soviets conducted their first successful atomic test. This would also be before
The Marshall Plan was begun, if that matters, and before the
Blockade of Berlin.
