[Bogolyubski]

I think that's a pretty good analysis as well. The setup of the tetrarchy really bought time for the Eastern half to stabilize. They also didn't have the degree of barbarian invasion that the west had to deal with, which might have been a factor as well. By Justinian's time, a good section of the west had even been reclaimed. The West was abandoned with the advance of the Muslims in the mid-600s, though.

[goldstategop]

Justinian's mistake was to try to reclaim the West instead of devoting imperial resources to stabilize and fortify the Empire's new borders. If he had chose the latter course, Islam might not have penetrated as far West as it eventually did.

(Denny Crane: "Sometimes you can only look for answers from God and failing that... and Fox News".)