An Island Built for Trade
Dejima was an artificial, fan-shaped island constructed in Nagasaki's bay, completed in 1636. Initially built to contain Portuguese traders, it became the exclusive site of the Dutch East India Company (VOC) trading post from 1641 to 1859. For over two centuries, this 15,000-square-meter outpost was Japan's sole connection to the Western world. The VOC's meticulously kept records, or dagregisters, provide a detailed economic record of this period, documenting every transaction and ship that docked.
The primary function of Dejima was commerce. The Dutch imported goods coveted by the Japanese elite, including Chinese silk, cotton fabrics, sugar, and scientific books. In return, Japan paid primarily with its most abundant precious metal: silver. During the early 17th century, Japan accounted for as much as one-third of the world's total silver production. The VOC's records show a massive, sustained outflow of this bullion. In the period between 1615 and 1625 alone, an estimated 130,000 to 160,000 kilograms of silver left the country through Dutch and Chinese merchants at Nagasaki. This trade was incredibly profitable for the VOC, with initial profits exceeding 50%.
A Calculated Closure
The sheer volume of silver leaving the country did not go unnoticed by the Tokugawa shogunate. This massive outflow represented a serious threat to the stability of the Japanese economy. The scholar-bureaucrat Arai Hakuseki, advising the shogun in the early 18th century, analyzed trade records and came to a startling conclusion. He calculated that 75% of Japan's silver and 25% of its gold had been drained away through foreign trade.
This economic data provided a strong rationale for the sakoku, or "closed country," policy. While often a purely isolationist measure to prevent the spread of Christianity, the VOC ledgers show it was a calculated act of economic self-preservation. The shogunate took direct action to stem the financial bleeding. In 1668, the export of silver was officially banned. Trade restrictions tightened over the years; in 1715, the number of Dutch ships allowed to dock annually was cut to just two. The primary export shifted from silver to copper, camphor, and porcelain. Arai Hakuseki implemented the Kaihaku Goshi Shinrei, a new set of trade rules that specifically required payment in goods like silk and porcelain rather than precious metals. The detailed financial data from Dejima gave the shogunate the evidence it needed to seize control of its monetary future.