Prior to the 1400s Europeans lacked the ability and technologies to explore foreign lands. The crusades had introduced the Europeans to luxury goods, however after the Crusades ended, Europeans continued to demand the same products. The Muslims and Italians controlled the trade of these goods and prices were uncannily high because the Muslims sold Asian goods to Italian merchants, and Italian merchants then sold these items to Europe at outrageous prices (Age of Exploration). The Europeans needed to find a direct sea route to Asia to keep the prices low.
Europeans not only had a strong desire for these luxury items and wealth from trade, they also thought it was their sacred duty to spread Christianity and convert non-Christians throughout the world (Age of Exploration).
The Portuguese led the way to foreign countries by building a monopoly over the Indian Ocean trade in the early 1500s. Even then the Portuguese looked further east to capture Malacca in 1511, and several years later the Spice Islands (History). They also began a trade with the Japanese, making them the first Westerners to visit Japan.
In Japan trade flourished, however in 1549 Christian missionaries began arriving, and by 1600 European missionaries converted around 300,000 Japanese to Christianity (Japan). Tokugawa Ieyasu, the first shogun of Japan did not agree with the missionaries actively seeking converts, which rivaled Japanese beliefs. He banned Christianity from Japan, but it resulted in many religious uprisings and rebel groups forming, causing many deaths (Japan). The shogun also worried that the Europeans would be able to gain control of the Japanese trade like they did with the Indian Ocean trade. The Europeans past ability to conquer and take control of trade as well as their ruthless Christianity conversions left Japan with only one feasible option, to isolate themselves.