There are many accomplishments that could be credited with helping the Roman Empire succeed. Let us look at three.
First, there is the establishment and organization of the Romany army. This army was so much better organized than other armies of the time that it was able to conquer essentially every enemy it met.
Second, there is the building of the roads that crisscrossed the empire. These roads were vital to Rome’s success for at least two reasons. First, they allowed the army to move men and supplies relatively rapidly to many places. Second, they allowed for the trade that helped the empire to prosper.
Finally, there was the creation of a system of government that was able to survive for such a long time. Rome’s government certainly had flaws, but it was able to remain in relatively good control of the empire for centuries.
These accomplishments were tremendously important to the success of the Roman Empire.
The Roman Legions were primarily the reason of why the Roman Empire was succesful.