I think it will be The Solar Eclipse and there will be a major Earth Kingdom victory that will help them win the war, but it of course won't be defeating Ozai or anything, just a major victory that takes out a really good army or something. I also think that gang will go to Omashu(New Ozai) and help the earthbenders fight the firebenders and take back Omashu. But after all of this the Fire Nation will come back still very strong, and the beginning of season 3 could be about some major battles that take place while the gang are at the battles. Or, I could be completely wrong about everything.