The Hongxi Emperor is a character in Book One (Awake to Emptiness) of The Years of Rice and Salt.

According to Wikipedia (http://en.wikipedia.org/wiki/Hongxi_Emperor )
The Hongxi Emperor (August 16, 1378–May 29, 1425) was an Emperor of the Ming Dynasty in China. He succeeded his father, Yongle, in 1424.
Yongle's eldest son Zhu Gaozhi was born August 16, 1378 and was educated by prominent Confucian tutors. He often acted as regent at Nanjing or at Beijing during his father's northern military campaigns. As soon as he became Emperor Hongxi in September 1424, he canceled Zheng He's maritime expeditions and abolished frontier trade of tea for horses as well as missions for gold and pearls to Yunnan and Annam. He restored disgraced Confucian officials and reorganized the administration to give high ranks to his close advisors. Hanlin academicians became grand secretaries, and they dismantled his father's unpopular militaristic policies to restore civil government. Hongxi improved finances by canceling requisitions for lumber, gold, and silver. Taxes were remitted so that vagrant farmers could return home, especially in the overburdened Yangtze River Delta. Hongxi appointed a commission to investigate taxes. He overruled his secretaries by ordering grain sent immediately to relieve areas of disaster. He ordered the capital be moved back to Nanjing; but Emperor Hongxi died, probably of a heart attack, a month later in May 1425. His son had been declared heir apparent and became Emperor Xuande at age 26. Although Hongxi had a short reign, he is credited with reforms that made lasting improvements, and his liberal policies were carried on by his son, Xuande Emperor.

References
Robinson references the Hongxi Emperor in Book One (Awake to Emptiness) on pages 68-79.
Robinson references the Hongxi Emperor in Book One (Awake to Emptiness) of The Years of Rice and Salt in order to signal the end of Zheng He's expeditions and China's influence and presence in world affairs. Although the Hongxi Emperor made lasting improvements and reforms, these were only apparent in China, and he removed himself from being a major palyer on the world stage and turned inward to deal with problems at home. Hongxi's appointment to the throne temporarily ended China's influence and presence on the world stage.