Final answer:
China and Japan became isolationist to preserve national identities and control foreign influence. The Ming dynasty's efforts to reverse foreign occupation and Japan's 'sakoku' policy both aimed to limit trade and the potential erosion of societal values due to European pressures.
Step-by-step explanation:
The isolationist policies in both China and Japan were influenced by several factors, including the need to preserve their national identities and to control foreign influence. China's turn towards isolationism can be traced back to the Ming dynasty, where the Hongwu Emperor attempted to reverse the effects of foreign occupation after the defeat of the Mongols. He limited trade to the exchange of tribute goods and ended private foreign trade in 1371. By the seventeenth century, harbors were fortified to prevent foreign trade and ships were destroyed. Japan's isolationism, known as 'sakoku', similarly restricted foreign contact and trade to specific, controlled ports.
While the decision to become isolationist for both nations stemmed from various reasons, a significant one was the concern over losing their cultural identity and the potential undermining of their societal values due to European cultural influences and trade pressures. Historians suggest that a spirit of isolationism in the court, the extravagances of Yung Lo, and Neo-Confucian prejudice against expansion were some reasons behind China's isolationist policies. Japan, on the other hand, needed to alleviate scarcities of natural resources and secure food supplies, leading to the country's militaristic government restricting foreign influence to maintain control.