Context: For a brief period in the 1790s, the British tried to establish a rival foothold on an offshore island, at Bolama. But by the 19th century the Portuguese were sufficiently secure in Bissau to regard the neighbouring coastline as their own special territory, also up north in part of present South Senegal.

Question: Who tried to establish a rival foothold at Bolama?
Answer: the British

Question: When was a rival foothold  attempted at Bolama?
Answer: the 1790s

Question: Who regarded Bolama as their own in the 19th century?
Answer: the Portuguese

Question: What other area did the Portuguese regard as their special territory?
Answer: part of present South Senegal

Question: What rival did the Portuguese fend off in Guinea-Bissau?
Answer: the British