Don't think of one region being dominant over another. This is the old simplistic approach to history. Instead, think of one royal family being in control over both regions and deciding which areas they are going to develop in any given time period and which ones they are going to neglect.
From a recent post:
"The dynastic period in Egypt and Sumer began as late as 1159 B.C. This date is that of the next known catastrophic event after the eruption of Thera. It does not pose a problem for me personally. All of dynastic history will fit comfortably after this date, but it dashes any remaining hope of acceptance for this model. Reality is not within socially acceptable bounds for potential solutions and therefore cannot be considered by any scholar who works within a social context, i.e., any university or proper institution!"
© Charles N. Pope, US Library of Congress. All rights reserved.