Complex sentence: The Portuguese paid 350,000 golden "ducados" to Spain and secured their presence in the islands, which not have been a necessity, as Portugal was actually entitled to the islands, according to the Treaty of Tordesillas.
Split into simpler sentences: The Portuguese paid 350,000 golden "ducados" to Spain and secured their presence in the islands. This payment should not have been a necessity, as Portugal was actually entitled to the islands, according to the Treaty of Tordesillas.