The Nobility War, sometimes referred to as "The Third Civil War", is a conflict that shook the Empire of Mankind between 33,580 CE and 33,955 CE (13,414 ALD - 13,789 ALD of the Lewisian Calendar), soon after the birth of the Empire, when after millenia of peace and prosperity, the Nobility had become so powerful to even challenge the Emperor himself. The Emperor tried to tied in control looking for ways to centralize and take power for himself, taking it out from the Nobility. This led to open revolt from some of the Nobles who saw their power, economic strength, status and influence decline by what they saw as an autocratic and dictatorial ruler. This war happened 4932 years after the end of the Second Civil War, after a period known as the Rule of the Twelve Emperors.
Several Emperors had previously tried to manage the balance of power between the rising aristocracy and their own power by cutting off the nobility's personal wealth, their range of action and their political influence inside the matters of the Empire. Sometimes even, noble property was confiscated.
The war was very hard, costly and bloody, and in many places in the Empire, entire noble families were wiped out and others lost a lot of their former glory and power. Some of the nobility escaped the Emperors persecution alongside several refugees from the war, forming the Plutocracy of Gish in 33,956 CE.
This war ended with the Emperor winning, making Thardos II the hard decision of forcing the Nobility to reside in Elpida, inside the newly created Imperial City. By doing so, noble families were easily controlled. All noble families had to dwell in Elpida, while the Head of each family could come and go from their planet to the capital. The Family could also go to their Planet and live there, but while doing so, the Head of the Family had to stay in Elpida so that at all times, Family and Head of Family could not be at the same time away from the Emperor and the capital other than with a special permit of the Emperor himself. The only place were both parts of the family could be together was actually in the Capital.
This laws were lessen with time as nobles proved loyalty and were more constraint in power by the rule of law. Tougher laws were pass, so that the Nobility was very much constrained by the Emperor. After several millenia, specially during the War against the Union, the Nobility was allowed more flexibility, and while they had to live for a period in the Emperor palace, Head of Family and Family could live together in their home system or planet.