How did the roman empire change over time?

The conquest of most of the Mediterranean between the 2rd century BC and 63 BC, during the period of the Roman Republic, was due to Rome winning a number of separate and unconnected wars which were fought for different reasons. It was not due to a grand design of conquest and imperial expansion. The first conquest which was deliberate was that of Gaul, which Julius Caesar set out to conquer in his Gallic Wars (58-50 BC). As a result of this the Republic was poorly equipped to deal with having an empire.

There were unsatisfactory administrative arrangements. The generated wealth was concentrated in the hands of the rich and newly enriched people. There was flaunting of wealth and corruption. The governors of the provinces (conquered territories) acted as if their provinces were their personal fiefs. Military commanders used military violence or the threat of it to obtain what they wanted. As a result the Republic was torn by a series of civil wars. The Republic fell under the weight ofunplanned imperial expansion.

Following the demise of the Republic, Augustus created rule by emperors. He added territories to the empire. Some client states of Rome were annexed. Some areas were annexed because they came under attack by invaders or because there were rebellions. The Alpine area was conquered to add a defensive buffer north of Italy. Augustus completed the conquest of Spain by defeating the Cantabrians in the northeast of the peninsula. Roman expansion into Spain was not due to a grand design of conquest either. It was due to wars against Rome by peoples who lived in areas of Spain who resisted the expansion in Roman activities and settlement in the peninsula. Under Augustus there was the conquest of southern and central Germany. This was a deliberate conquest. However, it backfired. Three legions were routed and Augustus withdrew back to the old frontiers.

The emperor Claudius annexed northern Morocco which was already a Roman client state. He also organised the invasion of England and conquered the south. The conquest of the north was commissioned by Vespasian. Trajan conquered Dacia (in modern Romania) because the Dacian king kept attacking the empire. Trajan also fought a war against the Persian Empire and took Mesopotamia Iraq) from them. However, his successor, Hadrian, gave it back to them because he pursued a policy of peace and because he thought that Rome could not hold on to this area.