Linked from
The 10 pages that link to Gulf of Tonkin, each with the reason it gives.
GuangxiRelated: Its coastline gives Guangxi access to maritime routes and ports.
Red River DeltaRelated: The rivers of the delta discharge into this gulf.
Qiongzhou StraitRelated: The strait opens westward into this gulf.
Leizhou PeninsulaRelated: The peninsula’s western coast borders this gulf.
HaiphongRelated: The gulf gives Hải Phòng its maritime outlet and regional sea routes.