A war of about a decade between the Talaxians and the Haakonian Order, ended in 2356 when the Haakonians used a weapon called the Metreon Cascade on the moon Rinax.
The war was drawing towards its tenth year when the Haakonian scientist Ma'Bor Jetrel completed the Metreon Cascade. It was used on Rinax, a populated moon of Talax, where it killed more than three hundred thousand people outright and left many more to die slowly of metremia. Talax surrendered the next day.
Neelix lost his parents and siblings on Rinax. The Voyager episode Jetrel, set fifteen years later, brings the scientist aboard claiming that Neelix may carry the disease. He is in fact dying of it himself and hopes to use the transporter to restore the vaporised victims, an attempt that fails.
Neelix confesses that he was not fighting that day but hiding from military service, and forgives Jetrel before he dies. The episode Mortal Coil returns to his memories of his sister Alixia.