Scythia - the revolving door into Europe

Before the days of planes and political asylum, the most common way into Europe was via an area known historically as Scythia - the Danube Basin (Scythia Minor) and the Pontic-Caspian steppe (Scythia Major).  

As I have been writing up a masters thesis on the missionary work from Constantinople, again and again this area and this phenomenon has been relevant. I have identified several phases of the occupation/settlement of these areas. As I am able to access more data and scholarship, I hope to expand the information below with authoritative maps. 

1. Goths and Huns (from 376) 

2. Gepids and Cutrigurs, Utrigurs and Bulgars (from 453) 

3. Slavs and Avars (from 557) 

4. Bulgars/Bulgarians and Khazars; the so-called Pax Chazarica (from 630) 

5. Pechenegs and Cumans (from 10th century) 

There were earlier and later phases of this phenomenon (i.e. pre-IV century and post-XI century). 

In many cases the peoples dominant in this area either went on to migrate into Europe, or lost their ethnic identity vis-a-vis newly dominant peoples. A primary example of the latter would be the Avars who, following their unsuccessful siege of Constantinople, were absorbed by their Slavic neighbours and in the 'reconquest' of the Balkans by Constantinople.