In 2 Chronicles 36:20, the exiles served Babylon's kings until which kingdom came to power?

Answer: Persia

The exiles served Nebuchadnezzar and his sons until Persia rose; Cyrus king of Persia then let them go up to Jerusalem.

“Those who escaped the sword were carried by Nebuchadnezzar into exile in Babylon, and they became servants to him and his sons until the kingdom of Persia came to power.”— 2 Chronicles 36:20 (BSB)