Rival military powers were ruthlessly destroyed, and conquered peoples were plundered that Rome might be great. During the period of rapid expansion Roman rule was always harsh and often corrupt. The only benefit it offered was the gradual extinction of international warfare, and it was difficult for suffering subjects to see that this was much of a gain. But as the position of Rome became more secure, and as Roman political institutions became more stable, the character of Roman government improved. Partly from the Greek philosophers, partly from their own experience, the Romans developed the concepts of a fundamental law binding all men, and of an ideal justice in which all should participate. Inspired by these ideals, guided by the great emperors of the second century A.D., the Roman Empire lost its predatory character and became a universal commonwealth. Inhabitants of Rome and Italy lost their special privileges, the rights of Roman citizenship were extended to almost all subjects of the Empire, and the provinces flourished in the peace and security provided by an honest and efficient government. As distinctions between conqueror and conquered disappeared, the Empire was accepted by all its subjects as a desirable and permanent form of political organization. Yet just as the Empire succeeded in creating a real community of interest and feeling in the Mediterranean basin, it began to decay. This decay is one of the great puzzles of history, and no one has ever been able to explain it in a completely satisfactory way. A partial explanation may be suggested by a discussion of certain weaknesses which existed in the Empire.
The most obvious weakness of the Roman Empire was political. The Republic had failed because it could not keep its officials from fighting for the spoils of power. Under the Empire this danger was avoided by steadily increasing the power of the emperor until no other authority in the state could resist his orders. But the imperial office was at first considered a temporary expedient and it never was placed on an absolutely permanent basis. This was especially true when it came to the question of succession. The new emperor might be the real or adopted heir of his predecessor, he might be