Airplanes, yes. Much of the strategic thinking about nuclear weapons was initially developed in the context of dreams about heavy bombers — the idea that if you could hit cities indiscriminately with them, that nobody would be able to tolerate it, so some kind of either deterrence or enforcement would develop. Obviously it didn't work out that way, but you can see the flip side of this thinking in WWII, where both Allies and Axis believed that targeting civilian populations from the air ought to bring a swift end to the war. In fact, except in the case of the atomic bombs, nobody thinks that this happened; even in the case of the atomic bombs, it is debatable whether the bombs by themselves would have brought about that effect (the entire debate about whether you can win a war from the air or whether you require "boots on the ground" continues today, but very few people think you can actually win a war without land forces).

There is a very curious but interesting book by Sven Lindqvist called A History of Bombing that outlines the move that took place from bombers to nuclear weapons in terms of this particular belief.

I don't recall similar sentiments about gunpowder (which is way earlier than all of the others on your list — European powers were using gunpowder weapons in the Middle Ages) or machine guns. The biggest argument that one sees regarding this pre-bomber is that the global economy won't tolerate a war — that countries were too intertwined to go to active war anymore. This sentiment was common even right before the beginning of World War I, which dashed its optimism.