The correct answer is option B) 15th century.

- China retreated into isolation during the 15th century.
- This period of isolation is often referred to as the Ming dynasty's isolationist policy.
- The Ming dynasty ruled China from 1368 to 1644.
- The 15th century falls within this period.
- The Ming dynasty implemented strict restrictions on overseas contacts and trade.
- This was done to prioritize domestic stability and limit foreign influence.
- The Chinese government feared that foreign trade and interactions could lead to political instability and social disruption.
- As a result, China limited its maritime activities and trade with other countries.
- The Ming dynasty implemented various policies to restrict overseas contacts.
- They banned private overseas trade and limited official trade to a few designated ports.
- They also implemented a strict licensing system for foreign merchants.
- Chinese ships were prohibited from sailing beyond the Indian Ocean.
- The Great Wall of China was also strengthened and extended during this time to further protect China's borders.
- This isolationist policy continued until the 16th century, when China's attitude towards international trade began to shift under the Ming dynasty's successors, the Qing dynasty.
- The Qing dynasty opened up trade and established diplomatic relations with various European powers.
- However, it is important to note that even during the period of isolation, China still maintained some limited trade and diplomatic exchanges with neighboring countries, such as Korea and Japan.
- The isolationist policy of the Ming dynasty had significant consequences for China's relationship with the rest of the world and its overall development during that time.