The grand adventure was driven from the top. Beginning with Henry the Navigator and continuing through John II and his son Manuel, royal support for the adventurers was essential because ships quickly wore out with worm, disease and battle thinned the ranks of the available adventurers, and organising new fleets took time. In fact you could say that building, equipping and directing ships was the main activity of the royal house of Portugal for over 100 years.
Getting access to markets in India was difficult, hence the violence. As Afonso de Albuquerque - Manuel's foremost Governor of India - found, without force there was no doing business on the continent. Trade up to that point had been controlled by Hindu potentates and Muslim merchants, and they guarded their prerogatives jealously. In order to gain access to supply of spices - mainly spices but in other goods as well - it was usually necessary to bring force to coerce submission among the existing powers. Dislodging the Muslim merchants meant putting pressure on the Hindu rulers, and fighting battles against them.
Albuquerque was an interesting man who attempted to bring new ways of doing things to the colonial project. Instead of the traditional Portuguese method of fighting man-on-man with a two-handed sword, for example, he worked to train troops in the new methods pioneered by the Swiss, who used pikes and muskets in tight formations. He also encouraged miscegenation, probably initially as a way to domesticate and control his troops, and he did it against the advice of the Church. He furthermore tried to bring a more sophisticated notion of office to the colonial project, and to stamp out corruption. But because of his innovations he was not always popular. He was also mortal, as were the kings.
There are other men to focus on in Crowley's book but Albuquerque is without doubt the most extraordinary among those the kings sent out to build an empire in a foreign ocean. His decision to take and keep Goa, for example, helped the Portuguese to maintain a trading station in India for 400 years, although others tried to bring scant forces to bear on different parts of the Indian coastline. Albuquerque also tried to fulfill Manuel's messianic vision of eradicating Muslims from the Middle East and retaking Jerusalem, although he notably failed to do so. After Manuel's death there was no king able to continue the colonial project with the same zeal and things began to fall apart. Eventually the Dutch and the English would take over where the Portuguese left off.
In many ways this is not a pleasant story. Third-world revisionists nowadays will have quite different takes to promote, but Crowley does not obscure what is not useful to the main thrust of his story, and is quite candid in his judgements of these often cruel men. What the story shows is that incredible things are possible even for small groups of men who are organised with single-minded focus on an overarching goal. Given the right people and enough resources they can achieve amazing things, as these adventurers most certainly did.