What new power in Mediterranean and threatened Greece?

The new power in the Mediterranean that threatened Greece was the Roman Republic. The Romans had become the dominant power in the western Mediterranean by the end of the 3rd century BC. As they expanded their territory, they began to come into conflict with the Greek states. In 146 BC the Romans conquered Macedonia, which was then the most powerful Greek state. The Romans then went on to conquer the rest of Greece, which became a Roman province.