Roman constitution wasn't prepared for the addition of ever more more provinces especially that of Asia. They were great in warfare but not some much in political change.They begin fighting with each other having civil battles and other countries. Rome became an Empire after Octavia put down his powers under the republic in 275 bc and stepped up as the first Emperor. Fact Octavian was later given the name Augustus meaning great, venerable.
Western Roman Empire
Military problems:
At the end of the fourth century, the Western Roman Empire destroyed at 500-year run as the world's greatest power. The collapse on military losses sustained against outside forces. In 410 the Visigoth King Alaric successfully destroyed the city