De fire nasjonene lvede i fred, (helt) til Ildnasjonen angrep*

If anyone's interested: http://www.nickelodeon.no/program/215-avatar-legenden-om-aang/videoer/7789-gutten-i-isfjellet

hes our hero, gonna take pollution down to zero

We have that one too!

Not 100% since I'm not Norwegian, but if it's the same difference as in Dutch, "ild" will be the phenomenon/element of fire, useful fire, or fire in general, (e.g. the pan is heated by the fire) while "brann" is uncontrolled, dangerous or damaging fire (e.g. there was a fire downtown).

ild is the element fire, or it can be flame. brann is uncontrolled or accidental fire, it could be oil in a pan or a house, or a forest fire. Norwegian has many words for fire: fyr, bål, ild, brann, forbrenning... And even more, if you speak of lighting it!

Luft er air.