Western Europe in 526. Can you find Italy? Yes. England? Yes. Span? Yup. Sure, Germany's missing and there are some smaller states that have since disappeared, but there's nothing too surprising. You can probably even guess what happened to the Burgundians. (Hint: they're still there.)
Fast forward about 500 years, to 1092. Germany, (AKA the Holy Roman Empire,) has joined the party. Spain's off doing something confusing (it's been conquered by Muslims via Morocco, leading to centuries of fighting and eventually some genocide and ethnic cleansing and the re-assertion of Catholic dominance and political unity, etc.,) but the other major countries look rather like they do today.
Here's a map of Eastern Europe/Western Asia from the same time period (c. 1015):
The Rus you can probably guess = Russia, but why are there two Bulgarian states? Who are the Pechenegs, Oghuz, Kimak, Kipchak, Karakhanids, Ghaznavids, etc? Where did they go?
Many of these people weren't just absorbed; they were displaced. The Cumans, once allies of the Kipchaks, eventually settled in Hungary. They came originally from East of the bend in the Yellow River, in China. The Mongols displaced them; they displaced others.
The Pecheneg displaced the Khazars, once a Turkic-speaking Jewish state north of the Caucuses.
In the 1800s, the Circassians, a group from the Caucuses, were famously beautiful. Hair dye ads in America pomised their products would turn users as beautiful as Circassians. In 1864, the Russians conquered and ethnically cleansed the area (many went to Turkey.) Circassia is no more.
So, students of Western Europe: count your blessings. You've got it easy.