During the preceding century of fighting along the length of the Perlemian Trade Route, the Republic had gradually gained the upper hand in its war with the Tion. Its superior industrial resources and the aid of the Jedi enabled the Republic to weather the fanatical tactics adopted by the increasingly desperate Tionese, and the Republic navy was able to fight its way to the Union's capital of Desevro.
Knowing that defeat was inevitable, the Desevrar rulers attempted to surrender. The Republic's leaders, however, had become enraged with the Union's tactics over the course of the war (including suicide attacks) and were determined to make an example of the Union's capital world. They ignored all offers of surrender from Desevro, and virtually sterilized the planet with pressure bombs.
The Tionese War ended with the razing of Desevro. Having been turned into a blasted wasteland, Desevro remained defiantly independent, but the rest of the Tion Cluster were intimidated into joining the Republic.
The brutal conduct of the Republican military at Desevro led the Jedi Order to break its official ties to the Republic, though the Jedi continued to protect the Republic's vulnerable frontier near Tionese space.