Many governors, especially those in remote parts of the empire, who were already ruling like sovereign kings, openly revolted.

He was sovereign king or chief, who deposed the indigenous chief, Kapawa.

Sithu Kyawhtin soon acted like a sovereign king of this remote region.

He was the sovereign king or chief of the Big Island.

Bali rules as the sovereign king of Patala.

He was the sovereign king or chief of the island of Maui.

How could he speak so to sovereign kings?

The second verse first mentions the sovereign king (lines 3-4):

Note that Parama-bhattarka indicates a sovereign king, who is not under a higher king.

In a certain sense, they consider themselves sovereign kings in their own right.