How did a spice contract turn into the Dutch conquest of the Banda Islands?

A monopoly treaty the Bandanese did not understand, and a governor-general willing to use force. Until the mid-19th century the Banda Islands were the world's only source of nutmeg and mace, and the trade was highly profitable: spices sold in Europe for 300 times the purchase price in Banda. That justified the expense and risk of shipping them.

Banda ran its own affairs. Before the Dutch invaded it was governed by an oligarchy of orang kaya, "rich men", and the Bandanese had an active and independent role in trade across the archipelago. They never allowed the Portuguese to build a fort. Rival Dutch expeditions united to form the Dutch East India Company, the VOC, in 1602, and some orang kaya were persuaded to sign a treaty, the Eternal Compact, granting the Dutch a monopoly on spice purchases. They had little understanding of its significance, and not all leaders had signed. The English were paying higher prices, which undermined Dutch aims.

In 1621 the VOC governor-general Jan Pieterszoon Coen landed well-armed soldiers on Banda Neira, and within days they had occupied the larger island of Lontar. The orang kaya were forced at gunpoint to sign an impossible treaty, giving Coen an excuse to use force. Japanese mercenaries were hired to deal with the orang kaya, forty of whom were beheaded.

Exact numbers are uncertain, but of a population of roughly 13,000 to 15,000, around one thousand Bandanese likely survived on the islands as forced labourers. Most survivors fled as refugees to partner islands, including Kei Besar, where the Wandan people descend from the original people of Banda.