The Yuuzhan Vong are marching through the galaxy and the planet Duro becomes a flashpoint of conflict. Leia is ordered to lead a diplomatic envoy from the New Republic to Duro to seek terms. From prior experience, she knows the only terms the Vong will only accept their annihilation due to their machine-influenced culture, which the Vong consider an abomination. So she clandestinely leads a military force to Duro which stops the Vong from advancing further into the galaxy but fails to retake Duro.
Then representatives of the Yuuzhan Vong tap into the galaxywide HoloNet and propose peace terms themselves. They will advance no farther, and they instead to demonstrate on Duro the success of their terraforming, if all the Jedi are surrendered to them.