Yeah, the 440 to late 1400s were a regress for European civilization. The whole continent was a basket case and hadn't advanced at all, and often regressed from the complexity/organization of civilization of the Roman empire. Even some of the major battles of the time, had only few thousand combatant, not more than a couple of Roman legions. Kings couldn't field armies, even larger to ancient greece, or persian empire (we are talking about 400-500 B.C.). The regress in overall state structure and organization was astonishing.

It took the renaissance to change things up and for innovation and cultural progress to pick up. So, it was more than a 1000 years lost to petty warfare, destruction and general ignorance.

If the Roman Empire had endured, who knows how things would have evolved. We would have been a different civilization by now. We probably would have had colonized mars by now :)

Ps. The byzantine empire, the eastern side of the Roman empire, after the late 600s - 700s, was just a shade of its original, and kept losing territory and influence until it was just a city state conquered by the Ottomans in 1453.