This is a timeline that explores what could have happened had China not retreated into the policy of haijin, or "sea ban" that crippled the general power of the East in OTL's "Age of Discovery".
1368--The Hongwu Emperor takes power in China, moving the capital to Nanjing and forcing the Mongolian rulers of the Yuan dynasty to retreat to the steppes. He founds the Ming dynasty
1371 (Point of Divergence)-- In order to curtail piracy, the Hongwu Emperor considers a sea ban. However, he discards the idea, as it would hurt China's economic strength and legitimate traders. Instead, he meets with authorities of local powers, such as the Shogun Ashikaga Yoshimitsu of Japan, on strategies for defeating the pirates.
1398--The Hongwu Emperor is succeeded by the Jianwen Emperor
1402--The Yongle Emperor defeats the Jianwen Emperor and succeeds him. China is driven into economic failure. The Yongle Emperor comes up with strategies to revitalize the Chinese economy
1405--Expeditions westward set out from China, reaching India and the Timurid Empire. The Bengali government, suspicious, does not allow trade with China. Neither does the Vijayanagar Empire or many of the other Indian nations encountered. However, trade with governments in the Middle East is prosperous. Many Western texts (such as Nicomachean Ethics) are traded and translated into Chinese, thus sparking new philosophical and political movements.
1407--Not to be outdone, the Japanese government commissions ships to sail westward, finding the same areas and meeting the same reactions. Meanwhile, many Chinese merchants are in outrage due to the fact that much of India is closed to them, arguing for a coup inside these governments. Similar movements arise in Japan.
1410--China invades Bengal successfully, relying on temporary alliances with small, neighboring states. This provokes a race between China and Japan for colonies in India. Many Chinese traders settle in India, and the use of Chinese ideograms and language is increasingly common
1412--Japan successfully conquers the Eastern Gangas and some of the small states surrounding it. Similarly, many Japanese traders settle in India, and the use of Japanese ideograms and language is increasingly common.
Further Chinese and Japanese incursions into India occur. Such rapid expansion slows down after 1420, when Japan has conquered Gujarat, Reddis, and Sind; China having conquered the Vijayanagar Empire, the Bahmani Kingdom, and the Khandesh. The only remaining state in India is the Delhi Sultanate, which, alarmed by the growing power of China and Japan in the Subcontinent, mobilizes its army. In order to keep colonies, China and Japan sign a temporary alliance to defeat the Delhi Sultanate. This alliance breaks apart, however, once the Delhi Sultanate capitulates in 1424 at the Battle of Delhi. An agreement is reached--Japan keeps the northern areas of the Delhi Sultanate in order to connect its colonies, and China keeps the southern and eastern regions.