The Zantree Alliance was smeared in 2373 by the Kliges'chee, the first victim of the Kliges'chee Tsunami. Poong was bombed out of the class M category killing billions.
The Poong Species survived in small numbers on Zantree colony worlds - enough to evventually recover.
After the fall of the Kliges'chee, the former Zantree were adopted in turn by forming Far Sector of the Federation.
The Ane helped the Free Kliges'chee to rally and begin winning their war for freedom. The inter-Kliges'chee civil war took the pressure off the Zantree Alliance, which began to recover from the war time damage to their economies.
This caused a rift with the Youn and the Tabooists, which caused the Zantree Alliance to sputter and fade. The Poong, the Olympians and the Kee Joined the Federation and are strong members. Only the Youn refused when they learned their trade concessions would not be carried over.
It is not unusual to see numerous Poong in Starfleet and in space in the Far region. They're having a blast.