Friendly Islands (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">friendly islands</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tonga that I've seen before include "part of Polynesia" , "Tropic island" , "Pacific Ocean monarchy" , "Horse-drawn vehicle" , "South Pacific island group country" .)