The Second Battle of Onderon was one of the very last battles fought during the Mandalorian Wars, near-concurrent with the Republic's second assault upon the Dxun moon during the same period.
Although significant in the sense that the great walled city of Iziz and its inhabitants were liberated from several years under the Mandalorian yoke, the reconquest of Onderon was actually of secondary concern to the Republic in military terms. A sizable Jedi force was detailed for landing in and reoccupying the walled city circa 3960 BBY, but the vast bulk of Revan's troops were simultaneously committed to digging out the entrenched Mandalorian holdouts on the jungle moon.
The fighting intensified throughout the battle, as the Mandalorian troops were fractured and made many fighting retreats, trying to kill as many Jedi and Republic troops as possible.
The Mandalorian devastation would ingrain itself in the minds of the Onderonian people for years to come, creating a latent hostility against not only against their former oppressors, but also against the Republic itself: specifically, that by belonging to the Republic, they invited more misery upon themselves than by reverting to their old xenophobic isolationism. This festering fear would prove to be the seed of the later Onderon Civil War.