narrow bridge to the mainland in order to prevent them from leaving the island. Terminology Trade prospered during the period, and though relations and trade were restricted to certain ports, the country was far from closed. Even as the shogunate expelled the Portuguese, they simultaneously engaged in discussions with Dutch and Korean representatives to ensure that the overall volume of trade did not suffer. Thus, it has become increasingly common in scholarship in recent decades to refer to the foreign relations policy of the period not as , implying a totally secluded, isolated, and "closed" country, but by the term used in documents at the time, and derived from the similar Chinese concept . Rationale It is conventionally regarded that the shogunate imposed and enforced the policy in order to remove the colonial and religious influence of primarily Spain and Portugal, which were perceived as posing a threat to the stability of the shogunate and to peace in the archipelago. The increasing number of Catholic converts in southern Japan (mainly Kyūshū) was a significant element of that which was seen as a threat. Based on work conducted by Japanese historians in the 1970s, some scholars have challenged this view, believing it to be only a partial explanation of political reality. Before the Tokugawa, Toyotomi Hideyoshi had previously begun to turn against the European missionaries after the Spanish conquest of the Philippines began, and the gradual progress of the Spanish there led to increasing hostility from the Tokugawa as well. The motivations for the gradual strengthening of the maritime prohibitions during the early 17th century should be considered within the context of the Tokugawa 's domestic agenda. One element of this agenda was to acquire sufficient control over Japan's foreign policy so as not only to guarantee social peace, but also to maintain Tokugawa supremacy over the other powerful lords in the country, particularly the . These had used East Asian trading linkages to profitable effect during the Sengoku period, which allowed them to build up their military strength as well. By restricting the ability of the to trade with foreign ships coming to Japan or pursue trade opportunities overseas, the Tokugawa could ensure none would become powerful enough to challenge the 's supremacy. This is consistent with the generally agreed rationale for the Tokugawa 's implementation of the system of alternate attendance, or . Directing trade predominantly through Nagasaki, which