With the return route to Mexico established, a lucrative trade between the Philippines and Spain developed, but only up to a point.
In a way, that was hardly surprising—any lengthy oceanic passage chad its dangers. Outbreaks of scurvy were a matter of when, rather than if, and the trans-Pacific crossing was longer than most trade routes.
Others might have flooded flood the markets of Europe with exotic goods. The Spanish crown limited the trade to two galleons running back and forth across the Pacific each year. Later, that number halved.
Still, apart from disease and the countless other hazards that came with a twenty thousand kilometre passage, the route between Manila and Acapulco should have been reasonably secure.
In theory, Spain's enemies could only get at the ships by sailing around the bottom of South America or through the Portuguese hemisphere.
Over the next three hundred years, a handful of would-be assailants made their way through Magellan's Straits or around the Horn. Anyone coming the other way had plenty of lucrative targets to divert them along the way.
Another handful of hopefuls made their way to the Pacific shores across the Isthmus of Panama.
Still, the Manila galleons went about their business largely undisturbed. After their cargoes were discharged in Acapulco and carried across to Veracruz, the passage across the Caribbean Sea and the Atlantic was less secure from raiders.
So the Spanish tended to employ substantial treasure fleets on the second leg.
A single ship with a scurvy-ridden crew might be an easier target. Still, the inherent difficulties of intercepting it were enough to deter most would-be assailants. There were precious few known islands where crews that had made their way into the Pacific could recuperate, and none lay anywhere near the galleon's route. 1
Although they were aware of the most likely rest and recuperation station, Spain left Juan Fernandez unguarded until Philip Carteret attempted to land on the main island in May 1768.
So, unless someone succeeded in finding those interesting locations Marco Polo described, there was not much of interest in the Pacific before the middle of the 18th century.
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1 While the Hawaiian islands are the obvious exception to this generalisation, they remained "undiscovered" until James Cook's third voyage. In Themes and Variations, Discounting the Notion of Discovery suggests that the Spanish encountered the islands much earlier and declined to disclose the details.