Why did the Tokugawa shogunate keep Japan isolated from 1603 until 1853?
It is generally regarded that the shogunate imposed and enforced the sakoku policy (isolation)under which no foreigner or Japanese could enter or leave the country on penalty of death. this was done in order to remove the colonial and religious influence of primarily Spain and Portugal, which was perceived as posing a threat to the stability of the shogunate and to peace in the archipelago. The increasing number of Catholic Christian converts in southern Japan was a significant element of that which was seen as a threat.
