The political life during the Era of the Empire

The Roman Empire lasted five centuries passing through phases of development, crisis and recovery.
The Empire made the Roman system stable for a long period. All the populations of the Mediterranean bacin became part of the Roman territory. Agriculture and trade developed: the latter took advantage of a good road network and the use of a common currency in all the Empire, a sort of "modern common market".
There was the need of a new kind of power to control such diverse populations.
The power was centralized in one person, the Emperor. The ministries of the Republica Magistrates were assumed by the emperor or simply deprived of their powers.
The power of the Emperor was based on the army: the Empire was practically a military dictatorship.
For a certain period of time the Emperor ruled with the collaboration of the Senate, which in turn had the power to elect the Emperors. But soon this power to select the emperor returned to the army which imposed with force it choice.
Furthermore the Emperor could count on his followers: on his personal party, his family, collaborators and the freemen.
With the passing of time the provinces grew in importance and people from the province became members of the Senate and even Emperors. Later Caracalla gave the citizenship to all the freemen of the Empire.