fall of empire ======= dark age. no one of the time CIVIL unrest/war had leads to SIGNIFICANT technological advances.
Through all the Empires that have fallen, we only had a few "dark ages" i think:
The European Middle Ages (500-1500 AD)
The Greek Dark Age (1100 BC–750 BC)
the dark ages of Cambodia (1450-1863)
and the mayan Dark Age (900 AD)
Technology comes from need. War is war, and it brings about the need to be intuitive. during the course of world war I, military aircrafts made great strides in technology. It went from flying the plane over the enemy and dropping grenades, to automatic machine guns mounted behind the propeller, that shoot precisely, and only, when the bullet will go in between the propeller blades.
Also, it can be argued that The Medieval Dark Ages was not brought about only by a collapse of the empire, but by a widespread "awakening" in Europe. People thought little of Science and Technology and concentrated their lives on Christianity. Many books and records were burned... anything that didn't agree the Church's way of thinking in any way. Some who opposed the belief, for instance, that "god made things fall", and argued that there is a scientific explanation for it (gravity), that person would most likely be killed. There was no room for advancement during this time because they common philosophy during that era was directly opposed to scientific advancement.
The Renaissance fixed that though.