I always thought of it as "the thing you only have basic knowledge of because every semi-nerdy internet celebrity mentions it every once in a while". I've never actually met or talked to anyone who wasn't from North America who would read these things.

So I wonder how prevalent it actually is in the world.

No. It's all Manga everywhere else.

They sell decent on Brazil and although I like I don't collect. Manga is killing it.

Wonder why is that... Why are Americans the only people who like superheroes?

I never liked superheroes comics and can't really answer your question, but one thing is sure: many people all over the world love movies based on superhero comics.

I for one always wondered why Franco-Belgian comics are not successful or not published at all in USA (don't know about Canada - they might be published and successful in Québec). French and Belgian artists made the best Western comics after all (e.g. Blueberry, Durango) as well as many of the best and most influential Science Fiction comics (e.g. Moebius' works which influenced e.g. Blade Runner and Alien, Valérian et Laureline which influenced the Star Wars design), not to speak of hundreds of great adventure comics, funnies and semi-funnies (Astérix etc.), but most North-Americans never heard of them.

Manga are the only regional comics that managed to conquer the whole world (but even they didn't manage it before the 1980s).

A possible answer to your question might be: worldwide publishing limitations in the early days and superhero comics being a genuine North-American invention and phenomenon (though the latter theory doesn't explain today's enormous worldwide success of superhero movies).

Neither have I.

I think it's actually somewhat understandable. Despite the immense number of immigrants, Americans have always been rather resitant to foreign culture. Anime & manga being probably the only exception. But anything European... nope.

I guess it's possible... I wouldn't count superhero movies as a problem with this hypothesis, as the movies lack many of the bad things (in my opinion) comics suffer from.

Maybe it has something to do with American national identity. They always admired vigilantes and one-man justice. Romanticized criminals and violence generally. I don't see that in Europe very much. Maybe superhero comics were so popular because they hit this particular part of their national identity...

Superhero comics aren't very popular here in Romania, and I've never cared too much for them myself!

Superheroes used to be awesome and everyone wanted to be one. Now kiddies idolize rappers and gangsters and want to be like them.

'M from the Philippines. We don't have any medium that track sales so I don't know how popular western "comics" are, but from my personal exp, when I don't buy popular "hardcovers" during the 1st week of release ie Batman, Justice League, Avengers etc... then they'd most likely be sold out the ff week(fullybooked).
I waited weeks for the absolute blackest night because they immediately went out of stock. Then again, it's possible that they only order few stocks. Japanese manga is still way more popular here than American comics.

Superhero "movies" is a different matter though. Iic The Man of Steel broke the all time opening record in the Philippines which was held by the Ironman 3. The dark night, the avengers, etc are also big.

Crazy Americans and their comic strips like Diabolik...