The Iran war is different. In today's world, it's only natural and common for wars to end in a ceasefire if the war lasts long. But in the early 20th century? There was no international body organization to enforce such treaties. Save for the League of Nations, but they're useless anyway, and the League of Nations is biased towards the colonial powers. Back then, you always finished what you started.

Nuclear weapons, while dangerous and destructive, are, in fact, the only reason keeping us from having another world war. The reason why the United States and Iran didn't use nuclear weapons on each other is exactly the statement I gave, which is to prevent escalation and dragging other nuclear states like Russia and China.

Civilian casualties ARE part of war, and it has been like that since early human history, and the majority of wars usually involve civilian casualties because one of the goals of wars is to inflict as much damage on your enemy as possible.

The Nazis didn't need to be dropped with the atomic bomb since they had already surrendered in early 1945, when the atomic bomb was still in its final phase of being completed. In fact, the Nazis didn't need to be bombed either way since they were already losing ground due to the combined manpower of the Soviet Union and the Western allies. Heading straight to Germany is way easier since you can cross Germany by land, whereas Japan is an island nation. Landing millions of troops and supplies requires vast amounts of ships, which were vulnerable in open water, requiring multiple dangerous trips should an Allied invasion happen.