“War does not determine who is right, war determines who is left”, – Murphy’s Combat Laws.
The scale of civil/paramilitary resistance to occupation was incomparable. Belgium had its brave franc-tireurs that inflicted painful casualties onto advancing Germans to the point where the Germans decided they needed to make an example by shooting innocent civilians and destroying their property. Civilians in Iran either didn’t have the weapon or din’t feel compelled to try and help their overwhelmed troops. So beyond some sporadic rapes and violence that usually goes with wartime foraging, the Soviet and British troops didn’t see the point in making the civilians suffer more than necessary.
Iran could only dream of the war propaganda machine that the powers of Entente Cordiale possessed. Whatever crimes on the Iranian soil might have been committed, they didn’t come on record or weren’t used for whipping up nationalistic sentiments, and waned from memory.
Germans didn’t even try at first to cover up their own atrocities. They saw public executions as a warning for civilians not to get involved in resisting occupation. Therefore, plenty of pictures, witness evidence, documentation. And certainly, educated urban Belgians and their allies were in a much better position at documenting atrocities than
Iran, where poor illiterate farmers and shopkeepers made the vast majority at the time. As to Soviet Union of WW2, we learned the lesson from the WW1 Germans very well, and when messing with prisoners, or restive civilians, or class enemies we were always making sure there was not much evidence left.
War history is written by victors. We have to live with it.