is this Avatar quote become an idiom in your country ? "everything changed when the fire nation attacked"

I think you mean meme/joke not idiom. An idiom doesn't make sense on it's own, like "let's hit the road." This is a [well-known meme](https://knowyourmeme.com/memes/everything-changed-when-the-fire-nation-attacked) that a lot of people, at least on the internet, know.

I've never heard it myself but I don't know if I know any Avatar fans. No one has ever talked about it with me anyway.

I've never heard that but I've never seen Avatar and don't know anyone who has. Well some may have seen it but no one has mentioned it

In my humble opinion, there is a bit of a difference between a dumb meme and an idiom. The latter has more... universality, for a lack of a better term.

I'd think what is a "fire nation"? The first thought is it somehow related to Mars?

While there is a large fandom, that would understand the reference, it doesn’t make sense to say it randomly. If someone walked up to me and said it randomly I would immediately wonder what kinda drugs that person was on. If you said it during the intro of the show, I would think you’re a really big fan of the show

I feel like it was more popular like 10 years ago

> **is** this Avatar quote become Should be: Has this Avatar quote become

No. The f I’ve ever heard this quote - it was once, in the theater. Never again since.

"Has this Avatar quote...." not "Is this Avatar quote..." And no. It's a meme some people are familiar with. That's it.

I see it on the internet, but not real life.

It's just a meme, not a common idiom, and it's pretty much only on the internet in my experience. And kind of old at that.

If you are a certain age and watched a certain show as a kid, then yes.