heavily to pay for its mounting military expenditures. To sum up, the emperor, the aristocracy and the army were the three main ‘players’ in the political history of the empire. The success of individual emperors depended on their control of the army, and when the armies were divided, the result usually was civil war*. Except for one notorious year ( CE ), when four emperors mounted the throne in quick succession, the first two centuries were on the whole free from civil war and in this sense relatively stable.
Succession to the throne was based as far as possible on family descent, either natural or adoptive, and even the army was strongly wedded to this principle. For example, Tiberius ( - CE ), the second in the long line of Roman emperors, was not the natural son of Augustus, the ruler who founded the Principate, but Augustus adopted him to ensure a smooth transition. External warfare was also much less common in the first two centuries. The empire inherited by Tiberius from Augustus was already so vast that further expansion was felt to be unnecessary.
In fact, the ‘Augustan age’ is remembered for the peace it ushered in after decades of internal strife and centuries of military conquest. The only major campaign of expansion in the early empire was Trajan’s fruitless occupation of territory across the Euphrates, in the years - CE abandoned by his successors. *Civil war refers to armed struggles for power within the same country, in contrast to conflicts between different countries.