Why did the Roman Empire, Holy Roman Empire and Russian Empire collapse in a similar fashion with a period of civil war followed by the rise of smaller regional powers before consolidating into a single nation again?

The Roman Empire is well known for collapsing due to a period of civil war, then splitting into smaller kingdoms before being consolidated by the Ostrogoths. The Holy Roman Empire collapsed in a similar manner, being weakened by the 30 Years War, before the smaller German kingdoms consolidated into Prussia. The Russian Empire also collapsed in a similar fashion with the Russian Civil War followed by the consolidation under the Soviet Union.<br><br>What is the reason for historical empires being unable to collapse into smaller regional powers without eventually being consolidated?