There are a number of factors that make the Empire significant. First of all, the Romans were remarkably tolerant of cultural and religious differences, and did not force conquered people to adopt Roman religion or even language. They only required that they make no alliances with foreign powers and furnish troops to the Roman Army. They were not even required to pay Roman taxes.
Among its other accomplishments, the Empire established a codified system of laws which provided that all persons accused of a crime were innocent until proven guilty; that the accused had the right to confront his accuser in open court; and that a judge could set aside a law he considered unfair. This Roman system became the foundation of Western legal systems.
Agriculture was generally conducted on large farms known as latifundia, which were operated by slave labor. Crops grown on these large estates was used for export and thereby enriched the Empire. Profit from the trade allowed for immense wealth to flow into Rome itself which had running water and numerous other amenities.
Entertainment was provided free of charge at the circus maximus and the Coliseum where gladiatorial battles were often conducted. This was done in part to keep the idle poor pacified and prevent revolts. The poor were often fed at public expense.
Finally, slavery was rampant in the empire; although a slave could expect to be emancipated by age thirty if he had served his master well. Slavery was not based on race; in fact German and African slaves were highly desirable.
These are the major elements of the Empire; much more time and space would be required for a more elaborate discussion.
The Roman Empire had many features:
1. Their army was disciplined and well- equipped.
2. Their military tactics were good.
3. They had a large army.
4. They were a strong nation.
5. They had good trading features.
6. Provincial distributions made their rule better and stronger.
The features which made the Roman empire one of the greatest were
1. Their highly disciplined military
2. Their genius Generals
3.Their ruling system etc.
Specifically, I would like to know if it insisted that all inhabitants become Roman citizens, prevented foreigners from trading within the empire or set up a military draft to supply the army.