Sasanian Persia in the context of "House of Sasan"

Constantius II (Latin: Flavius Julius Constantius; Ancient Greek: Κωνστάντιος, romanized: Kōnstántios; 7 August 317 – 3 November 361) was Roman emperor from 337 to 361. His reign saw constant warfare on the borders against the Sasanian Empire and Germanic peoples, while internally the Roman Empire went through repeated civil wars, court intrigues, and usurpations. His religious policies inflamed domestic conflicts that would continue after his death.

Constantius was a son of Constantine the Great, who elevated him to the imperial rank of Caesar on 8 November 324 and after whose death Constantius became Augustus together with his brothers, Constantine II and Constans on 9 September 337. He promptly oversaw the massacre of his father-in-law, an uncle, and several cousins, consolidating his hold on power. The brothers divided the empire among themselves, with Constantius receiving Greece, Thrace, the Asian provinces, and Egypt in the east. For the following decade a costly and inconclusive war against Persia took most of Constantius's time and attention. In the meantime, his brothers Constantine and Constans warred over the western provinces of the empire, leaving the former dead in 340 and the latter as sole ruler of the west. The two remaining brothers maintained an uneasy peace with each other until, in 350, Constans was overthrown and assassinated by the usurper Magnentius.

The foreign relations of Imperial China from the Qin dynasty until the Qing dynasty encompassed many situations as the fortunes of dynasties rose and fell. Chinese culture had influenced neighboring and distant countries, while being transformed by outside influences as well as being conquered. During the Western Han dynasty, the Silk Road trade routes were established and brought Hellenistic Central Asia, Persia under the Parthian Empire, and South Asia into contact with the Chinese empire. During the 2nd century BC, Zhang Qian became the first known Chinese diplomat to venture deep into Central Asia in search of allies against the Mongolic Xiongnu confederation. Han Chinese attempts were made at reaching the Roman Empire and although the mission led by Gan Ying in 97 AD was a failure, Chinese historical records nevertheless maintain that the Romans traveled to southern China and Vietnam via the Indian Ocean. Buddhism from India was introduced to China during the Eastern Han period and would spread to neighboring Vietnam, Korea, and Japan, all of which would adopt similar Confucian cultures based on the Chinese model.

Following the fall of Sasanian Persia to the Rashidun Caliphate, Chinese contacts with the Islamic world were initiated during the Tang dynasty. Foreign faiths entered China at this time, such as Zoroastrianism, Nestorian Christianity and Islam, although Chinese Buddhism and Taoism remained prominent. The Song dynasty dealt on a basis of equality with the neighboring Liao and Jin dynasties until falling to the Mongol conquest. The Mongol Empire became the dominant state in Asia, and the Pax Mongolica encouraged trade of goods, ideas, and technologies from east to west during the early and mid-13th century. Marco Polo could safely travel back and forth, for instance. The Mongol-led Yuan dynasty founded by Kublai Khan ruled from the capital of Khanbaliq (modern Beijing). The Yuan dynasty's failed diplomacy with the Kamakura Shogunate of Japan led to the Mongol invasions of Japan, which also ended in failure for the Yuan Empire.