What were the consequences of isolation in feudal Japan?

Answer 1

Basically, Japan wanted total control over its religious, economic and political affairs, which is simply impossible when you have foreign missionaries and traders running around the country.

The leaders of Japan at the time (the shogun and his advisors) were concerned about the growing influence of European culture and religion on Japan. They knew how other countries had been colonized and "christianized" , and indeed, had seen examples of it starting in Japan. There were already powerful Christian Daimyo, and there were concerns that such a person might prove more loyal to their Christian leaders than to their Japanese ones (which of course did happen from time to time, look up the Shimabara Rebellion of 1637 for an example).

It was also to retain control over trade, but as we must remember, all European traders of that time were also carrying missionaries or served the same function themselves, so you got the religion with the trade, both of which the Tokugawa Shoguns wanted to control.

It took a while: from the early 1600 or so right up to its most isolated in 1650-ish, but at that point, Christianity had been pretty much wiped out and all foreign trade and traders were confined to one port in Nagasaki. Any non-Japanese going anywhere else was put to death immediately.

Answer 2

A distinctive way of life developed in Japan.