I don't buy it. Empires thrive when they are broadly expanding wealth, whether that's by plundering neighbors or making their economy more effective.

There's always a tension between growing the pie or taking more of the pie for yourself. If growth appears to be slowing and there's a lot of pie to fight over, more and more people will focus on the latter. Sometimes that's healthy, but without external pressure it usually takes the form of corruption, pettiness, and other destructive behaviors.