The Destruction of Tazino Prime occurred toward the end of the Second Shadow War.
After Sheridan's attack on Z'ha'dum, the Shadows dispersed their fleets to various points across the Galaxy. Unfortunately for those planets, being so openly touched by the Shadows, the Vorlons decided that they had become irreparably tainted by 'the darkness', regardless of if the worlds could have possibly refused the 'request' of a fleet of Shadow vessels. After their first target, Arcata VII was destroyed, they attacked and destroyed Tazino Prime.
The planet was completely destroyed making it uninhabitable for humanoid life.