Andu

When the Andu banish someone, the banishment is complete.
No Andu will have anything to do with the banished.
They cannot return to the Andu homeworld, and are not welcome at any offworld Andu establishment.
Andu medicines, Andu technologies, and Andu libraries are all off-limits to the banished.
Anyone who breaks the prohibition, knowingly or not, is subject to severe punishment by the Andu.
Which is why Andu civilization collapsed.
Everyone eventually was banished.
Except for one: Emperor Anduval the Third.
Alone in his palace with his robotic servants, sipping his wine, and watching triple-sunsets with a quiet heavy sigh.