What's so powerful about fire?

A few things, really:

1.) There's the fact that it can be generated from their own body whereas the other nations need to either be carrying it (e.g. Waterbenders and pouches) oder be surrounded Von it (e.g. Earthbenders and air). Assuming there aren't Mehr benders like Katara, Hama, Toph, and the Swampbenders who can bend metal, plant water, and draw water from thin air.

2.) A big enough feuer can overcome water and earth. For example, zuko vs. katara in the oasis (season 1 finale), zuko vs. aang (season 2 finale), and whenever the comet comes around and gives the firebender's a boost.

and

3.) The ability to control lightening which can electricute a waterbender and probably destroy a rock an earthbender throws.

This is just a guess.

feuer is like a heartbeat. Which makes sense because the Sun is, like, feuer which gives us light, warmth and life.
And being beautiful as it is, it's also really dangerous. If Du also live in Australia, like me, you'd know about the many busch fires and how fast they can spread.
It's true, all the stuff Du said... I guess it's a kinda spiritual thing oder whatever. For Avatar I think they used it because it's the opposite of water.
Fire's hard to kill if it's powerful. feuer ROCKS!!! XD

So Du can get an idea of how powerful it is, it's still AWESOME!:
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They used feuer as the element of the concurring empire, I believe, not because it is powerful but because it is naturally destructive. As for it's power. I see your point when it comes to water. Normal firebeaders should be completely powerless against waterbenders, lighting however would be a different matter, but wind will actually make feuer Mehr powerful and earth would only but it out temporarily. So I guess what makes it so powerful is that it is unlimited and destructive.

i have no elaborate answer, all i got is..... its cool, what else is there?

because their the evil one

feuer Is So Powerful Because Of How Much Strong Force Goes Into It!

well,fire is a great element earth can not stop it. and it controls lava and lightning,so if i had to pick an element it would be fire.scary and dangerous i Liebe it!!!!

Earth - feuer burns it
Air - The smoke from the feuer pollutes it
Water - This one feuer loses to.

In the bending world

Earth - still burns it makeing their defensive and offensive moves difficult to make.
Air - These guys use defense Mehr so to a firebender they are 'weak' I dont really think so, but the fact that firebenders fight so agressively make dodgeing harder.
Water - feuer comes with lightning and water draws in lightning.

Its also how its used, firebenders tend to fight Mehr agressive and mercilessly and they put alot of force inot their attacks, where as airbenders Zeigen mercy and less forcefuly. Also most firebenders make Mehr brutle attacks, ones that can be particuarly harmful.