In Avatar: The Last Airbender , the Fire Nation had captured a huge portion of the Earth Kingdom by the end of Book 2 , with fan discussions describing it as effectively controlling much of the west coast and north, though not every area was fully occupied all at once.

What that means

  • By that point, the Fire Nation’s reach was more like wide military control than a neat border map.
  • Key strongholds and major territories had fallen, but some regions still resisted or remained only lightly held.
  • The exact amount of land isn’t given as a precise canon percentage in the sources I found, so the safest answer is: most of the Earth Kingdom was under Fire Nation domination, especially the west and north.

Quick read

If you mean the Fire Nation’s takeover in the show, the best concise answer is: they had captured most of the Earth Kingdom, but not literally all of it.