"imperial mandate" is correct and usable in written English.
You can use it to refer to a decree or order given by a powerful ruler. For example, "The emperor issued an imperial mandate that all citizens must pay taxes".
In another tradition, however, Cao is said to have been in conflict with the law but mended his ways after his release from prison was arranged by an imperial mandate.
Although the kingdom of Iraq, which arose from the ashes of the Ottoman Empire, was under an imperial mandate only until 1932, the British retained significant control until the late 1950s.
Leo, needing the Imperial mandate for his campaign against what he viewed as a dangerous heresy, promised to assist in expelling the French from Lombardy, leaving Francis with only the Republic of Venice for an ally.
His royal and imperial decrees mandated the establishment of monastic and cathedral schools to teach both the laity and the clergy so that the fundamentals of the faith would be known to all.
When the Han imperial house finally lost its mandate to rule, Han Confucianism seemed lost and powerless in overcoming the forces of disorder that threatened to engulf the country.
Imperial information, an expression of heaven's mandate, was sacred.
Instead the brigade was assigned to the 6th Airborne Division, which had been named the Imperial Strategic Reserve, and sent to serve in the Mandate of Palestine.
In this way, Hakuseki attempted to validate the Confucian notion of the "mandate of heaven" and to undermine the idea that the imperial line, because of its divine origins, was the ultimate source of political authority in Japan (Nakai, 247-248).
Centuries of foreign imperial occupation followed, by Romans, the Muslim conquest, Crusaders, the Ottoman empire and the British mandate.
This is an ancient notion, dating back to imperial times, when an emperor's reign was believed to be legitimised by a so-called "mandate of heaven," (tianming), that conferred the right on a sovereign to rule.
This parallels in some ways the restraints on imperial behavior by Chinese dynasties that sought a perception of popular as well as divinely given mandates to rule.
