On hot roads that bake under the Tongan sun, a black London taxi cab used to split the traffic like it was parting the Red Sea. It was the personal vehicle of the late King George Tupou V.

NUKU'ALOFA, Tonga — Tongan Prime Minister Siaosi Sovaleni suddenly resigned on Monday, his office and parliament officials said, in the wake of a power struggle with the Pacific nation's royal ...