People don't always make rational decisions? I'd agree with you, but the times they don't make up a minuscule fraction of all times. When we have incomplete information we're left to make probabilistic approximations about how likely each possibility is the real explanation for something.

Operation Barbarossa is great example - I really enjoy WW2 history! You seemingly think this was an arbitrary act of a mad man. In reality it was a rational and calculated decision. The Red Army was amassing on Germany's border and it was later revealed that Red Army generals had already been requesting permission to begin their attack, but Stalin was waiting for a more strategic opportunity. In particular he wanted England and Germany to go to war and for his army to march over the remains. By contrast England in the west was wanting the exact same thing with the USSR and Germany. America was also looking more and more like it might take a more direct role in the war.

Germany basically had two substantial powers on either side of it, waiting to pounce. It had even offered peace to England, who rejected the offer, in an effort to avoid fighting a war on both sides. And both sides were also massively ramping up their forces. It was during this era that millions went without under Stalin as he dedicated massive and unprecedented resources to a military buildup. And England, as mentioned, was also receiving increasing support from America. In other words, his enemies were getting stronger faster than he was. His invasion was what he saw as the best of many bad options.

When there is an explanation that follows logically and clearly for something, and another explanation that simply relies extensively on illogical events and turning 'bad guys' into caricatures, I tend to go with logic. Could I be wrong? Like I said, absolutely. And I'm fine with this because history shows time and again that logic tends to be far more accurate than a one-sided perspective on events.

As a sort of edit here, to clarify - I am not equating rational with 'good' decisions. But only that decisions are generally driven by a reason. These reasons can be good, bad, flawed, or flawless. But there is a reason that generally can be empathized with, which is not to say agreed with.