Dawson Europe

The expansion of urban civilisation in the imperial age was, in fact, 

to an even greater 
extent than that of modern industrialism, a great system of 
exploitation which organised the resources of the newly con- 
quered lands and concentrated them in the hands of a minor- 
ity consisting of capitalists and business men;

https://archive.org/stream/makingofeurope00daws#page/32/mode/2up 

So long as the empire was expanding the system paid its way, 

for every new 
war resulted in fresh territories to urbanise and new supplies 
of cheap slave labour. But as soon as the process of expansion 
came to an end and the empire was forced to stand on the 
defensive against new barbarian invasions, the economic bal- 
ance was destroyed. The resources of the empire began to 
diminish, while its expenditure continued to increase. 

...

They 
saw in the Roman Empire the realisation of the traditional 
Hellenistic idea of the unity of the civilised world — the oecu- 
mene — an d they held up to the emperors the Stoic ideal of 
an enlightened monarchy in which the ruler dedicates his life 
to the service of his subjects and regards government, not as 
a privilege, but as a duty.