Up to 1974, the title of "Negus" was used for the traditional rulers of what country?

Question

Which country is made up of 176 islands, 36 of them inhabited, in 3 groups (called Vava'u, Ha'apai, and Tongatapu) which stretch north-south for 800 kilometers (500 miles)?

Answer 1

Ethiopia
It was also used, up to 1890, for the rulers of Eritrea.