Final answer:
The other great powers, particularly England, France, and the Netherlands, encouraged privateering against Spanish treasure ships in the Americas as they did not recognize the Treaty of Tordesillas which Spain and Portugal had signed.
Step-by-step explanation:
In addition to ignoring the Treaty of Tordesillas (1494) and Spanish claims to the Americas, the other great powers also encouraged England, France, and Netherlands to rob Spain's treasure ships sailing from Mexico to Peru. These European powers did not feel compelled to respect treaties that they had no part in and which were blessed by a pope they either did not recognize, as in the case of Protestant England and Netherlands, or simply chose to ignore, as in the case of Catholic France.
Their naval and privateering activities were aimed at weakening Spain's grip on its American territories and at diverting some of the immense wealth of the Americas into their own coffers. While Portugal had originally been part of the aforementioned treaties, signing them with Spain to divide the New World between them, they were not typically involved in the raiding of Spanish treasure ships.
Instead, it was England, under the rule of monarchs like Elizabeth I, and the Netherlands, with its well-trained sea captains and merchants, who posed significant threats to Spanish sea lanes. France, while not as aggressive on the seas as England or the Netherlands, still sought to establish its own colonies and trade in the Americas, often at Spanish expense. The economic and political rivalry between these nations was one of the key factors that led to a gradual erosion of Spanish authority in the New World.