The feudal system probably would not have developed if the roman empire continued. why?
europe would not have been considered worthy of attack by invaders.
the emperor would have kept peace, so there would have been no threat of invasion.
a strong military would have been in place to protect people from invaders.
the emperor did not believe the feudal system could protect people from danger.

The main reason why the feudal system probably would not have developed if the Roman Empire continued is because "A strong military would have been in place to protect people from invaders" since this is how the Romans kept peace in the past. 

A strong military would have been in place to protect people from invaders.

With the Roman Empire in place, the Roman army would have protected the empire from invasion. After the fall of the empire, Europe came under the control of new leaders but the new regions were weak. The feudal system provided landowners and peasants security through a lord and his military. This system protected lands in exchange for work and taxes.