Re: Khazars - yes their history is very interesting. They had a great Empire (in what is now primarily Ukraine and the Crimean peninsula) adjacent to the Byzantine Empire. See the change from about 650 to 800 CE.
http://en.wikipedia.org/wiki/Khazaria#Formation_of_the_Khazar_state
Seems to be a propensity for westward movement.
Thanks for the reference on Avars.
Here some more books to consider.
The Narrators of Barbarian History (A.D. 550-800): Jordanes, Gregory of Tours, Bede, And Paul the Deacon (Publications in Medieval Studies) (Paperback)
https://www.amazon.com/dp/0268029679/?tag=pfamazon01-20
The Gothic History of Jordanes (Christian Roman Empire) (Paperback)
https://www.amazon.com/dp/1889758779/?tag=pfamazon01-20
History of the Lombards (The Middle Ages Series) (Paperback)
https://www.amazon.com/dp/0812210794/?tag=pfamazon01-20
Barbarians and Romans, A.D. 418-584 by Walter A. Goffart
https://www.amazon.com/dp/0691102317/?tag=pfamazon01-20
Barbarian Tides: The Migration Age and the Later Roman Empire (Middle Ages Series) (Hardcover) * I have this one.
by Walter Goffart
https://www.amazon.com/dp/0812239393/?tag=pfamazon01-20
People and Identity in Ostrogothic Italy, 489-554 (Cambridge Studies in Medieval Life and Thought: Fourth Series) (Hardcover)
https://www.amazon.com/dp/0521571510/?tag=pfamazon01-20
The Early Middle Ages: Europe 400-1000 (Short Oxford History of Europe) (Paperback)
https://www.amazon.com/dp/0198731728/?tag=pfamazon01-20
Rome's Gothic Wars: From the Third Century to Alaric (Key Conflicts of Classical Antiquity) (Hardcover)
https://www.amazon.com/dp/0521846331/?tag=pfamazon01-20
Visigothic Spain 409 - 711 (A History of Spain) (Paperback) by Roger Collins
https://www.amazon.com/dp/1405149663/?tag=pfamazon01-20
Imperial Ideology and Political Thought in Byzantium, 1204 - 1330 (Hardcover)
https://www.amazon.com/dp/0521857031/?tag=pfamazon01-20
Book Description
This is the first systematic study of Byzantine imperial ideology, court rhetoric and political thought after the Latin conquest of Constantinople in 1204 - in the Nicaean state (1204-1261) and during the early period of the restored empire of the Palaiologoi. The book explores Byzantine political imagination at a time of crisis when the Empire ceased to be a first-rate power in the Mediterranean. It investigates the correspondence and fissures between official political rhetoric, on the one hand, and the political ideas of lay thinkers and churchmen, on the other. Through the analysis of a wide body of sources (some of them little known or unpublished), a picture of Byzantine political thought emerges which differs significantly from the traditional one. The period saw refreshing developments in court rhetoric and political thought, some with interesting parallels in the medieval and Renaissance West, which arose in response to the new historical realities.
About the Author
Dimiter Angelov is a Research Fellow and Lecturer in the Centre for Byzantine, Ottoman and Modern Greek Studies at the University of Birmingham. He studied at Harvard University and has also taught at Western Michigan University.
I'll also throught this one in. It's not too expensive.
Southeastern Europe in the Middle Ages, 500–1250
http://www.cambridge.org/us/catalogue/catalogue.asp?isbn=9780521894524
I think this is the book on Central Asia of which I'm thinking.
The Cambridge History of Early Inner Asia (Hardcover)
https://www.amazon.com/dp/0521243041/?tag=pfamazon01-20
http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521243049
Book on Google -
The Cambridge History of Early Inner Asia
FYI -
http://en.wikipedia.org/wiki/History_of_Central_Asia
The history of Europe is intertwined with that of Central Asia through the various migrations. Heather elucidates the impact of the Huns upon the Roman Empire and the 'barbarian' tribes who were situated between the Huns and Romans.