IT IS EASY enough to talk about Tokugawa Japan's uniqueness, with its domestic political stability, steady economic growth, controlled and peaceful foreign relations, and development of various social values and attitudes, all of which were sustained for two and a half centuries. However, strictly speaking, its uniqueness can only be fully appreciated when it is compared with the history of other countries. Such comparisons are rare and it is hard to think of any historian who has attempted to do so in any depth – with the solitary exception of Louis Cullen. Over the course of his fifty years’ career as a historian, he has conducted extensive research on the early modern history of Ireland, Britain and France, later extending his interest to Japan. He has written eight monographs plus five shorter studies and edited six volumes of studies in history or conference proceedings.

Cullen's ‘research’ is by no means confined to reading manuscripts at particular archives; importantly, he never uses documentary sources before he understands how they were created, preserved, copied or destroyed and, at times, went missing. Consequently, spending, as he has, a considerable amount of time and labour in Japanese as well as European archives and libraries has enabled him to compare the personalised and non-systematic way of record-keeping in Tokugawa Japan and the more formalised way of the European counterparts. In Japan, shogunal records were regrettably thin, while the papers of bakufu officials at Edo and elsewhere in the country were simply regarded as the personal property of individual office-holders. However, there was a positive side to the Japanese style of record-keeping. Because of the number of copies that had been made, often by private hands, compilation in later years was possible – as Cullen's careful tracking of Katsu Kaishū's editorial activities shows – which has enabled historians to catch a glimpse into the past even though the original documents no longer exist.

More specifically, Cullen's insight into sources is illustrated by his important study of the population figures of Tokugawa Japan, which, though no figures exist for three census years, survive in detail for eleven of the remaining nineteen. The data were collected by the domains and then converted by shogunal officials to a kuni basis before a grand total was arrived at.