Alternate history is an interesting business under the best. What would happen to much of history if superheroes appeared in it?
Much would depend on how powerful and how common they were. Marginal powers would mean they were not that much more dangerous than ordinary humans, and probably that a large enough force could cope with them. Superman-scale powers on the other hand. . .
If there were few of them, the side with Superman would win, if deployed with any amount of sense. If there were many, well, the wars might turn out the same, but the question is how would it affect the societies involved? Sure, you can hold off the neighbors with your three powerhouses, unless -- one of them decides he can do better with the enemy. There will be perks with power. It lends itself to an aristocratic society -- and the more superpowers there are the better they can fulfill that role in society. (Whether powers are hereditary would also complicate matters.)
Of course, if you hypothesized a mad scientist origin for heroes in general, that would explain the recent origin. 0:)