How did the geography of Japan isolate it from foreign influences?

Answer 1

An obvious answer is the fact that Japan has not been isolated from foreign influences except for a series of very select historical periods throughout the nation's history. Much of Japanese culture and, indeed, a majority of the genetic stock that makes up the modern Japanese ethnic group came from East and North Asia. China and Korea are the most obvious donors with the Kanji writing system, Buddhism, rice cultivation, ironworking, tea, and so on being introduced from these areas.

What I am assuming what you are referring to is the isolation period that coincided with the Edo Period or the Tokugawa Shogunate of the 17th to 19th centuries. In this instance, Japan was isolated from Western culture by it's geography in several ways.

First, Japan is one of the furthest areas from Europe to reach by sea travel. To get there at that period in time, one must have gone around the entirety of Africa, crossed the Indian ocean, then gone around and up the coast of Southeast Asia and China. The alternative would have been to cross the Atlantic to go through the dangerous Straits of Magellan at the southern tip of South America and then cross the entire Pacific Ocean. Either way, the journey was quite dangerous and very long.

Secondly, the presence of other, more lucrative targets allowed Japan to remain generally isolated for as long as it did. China was, of course, for the longest time the main interest of the Western trading nations in East Asia. Portugual originally started trading with Japan after finding the islands by accident because an embargo between Japan and China allowed the Portuguese to act as an intermediary, increasing their profits in trading with China. Then, when the European powers began colonizing Asia, Japan received mainly peripheral attention (ex. the Dutch on Dejima Island) because Europe was occupied absorbing their own gains in South Asia, Southeast Asia, and later Chinese concessions. By the time the West and it's cultural influence in the form of the US, UK, and France (Russia in the north) began seriously intruding in Japanese society in limited geographic areas, Japan was beginning to voluntarily Westernize on it's own, especially after the Meiji Restoration.

Answer 2

They kept all ports except one closed to foreigners.