Did Portugal break a spice monopoly in the Indian Ocean, or build a new one with a pass?

It did both: it broke into an existing trade, then built a monopoly of its own. Before the Portuguese arrived, Arab traders, mainly descendants of sailors from Yemen and Oman, dominated maritime routes throughout the Indian Ocean. Portugal did not simply open the sea. It created its own licensing system, the cartaz, in 1502, to control and enforce a Portuguese trade monopoly over a wide area.

The cartaz was cheap and looked like a favour. It was issued by the Portuguese at a low cost, granting merchant ships protection against pirates and rival states. But its main purpose was to ensure that merchants paid tax in Portuguese trading posts, directing them to Goa, Malacca and Ormuz, and guaranteeing the monopoly on the spice trade. Officially no vessel was permitted to sail on the Indian coast without it, on pain of losing its cargo, being attacked or even sunk; the ships targeted were mainly Muslim, Hindu and Malay merchants.

Force stood behind the paper. On Cabral's 1500 voyage, after an attack on his factory at Calicut, he seized ten Arab merchant vessels and killed about six hundred of their crew. Mamluk-Indian resistance was decisively defeated at the Battle of Diu in 1509, and in 1511 Albuquerque conquered Malacca, then the center of Asian trade.

It did not last. In the 17th century the Portuguese lost most of their valuable Indian Ocean trade to the Dutch and the English. The pass left one trace in language: it introduced the word kadalaas into Malayalam, where it is still used to denote any kind of paper.