"The first contact with the West occurred about 1542, when a Portuguese ship, blown off its course to China, landed in Japan. Firearms introduced by Portuguese would bring the major innovation to Sengoku period culminating in the Battle of Nagashino where reportedly 3.000 rifles (actual number is believed to be around 2.000) cut down charging ranks of Samurai. During the next century, traders from Portugal, the Netherlands, England, and Spain arrived, as did Jesuit, Dominican, and Franciscan missionaries."
http://en.wikipedia.org/wiki/History_of_Japan