However, they had to protect the shipping lanes in order to get their treasure home, and this meant keeping hold of as much of the Caribbean (or the  Spanish Main,  as it was then known) as possible.
Shipping lanes were well guarded from pirates.
mnli hypothesis: Shipping lanes were well guarded from pirates. premise: However, they had to protect the shipping lanes in order to get their treasure home, and this meant keeping hold of as much of the Caribbean (or the  Spanish Main,  as it was then known) as possible.