A few point to consider.
Roman empire basically static from the 1stC AD till its conversion to Christianity where things got even more hierarchical and eventually died through invasions of relatively unstructured Germanic "barbarians"; basically freemen.
However, Rome's development BC was characterised by a major challenge to class structure in which the Patritian class had to give way to the Plebians, and their Tribune representatives provided more power across the class divides.
Once the imperial aristocracy was established Rome did very little progress.
The British empire when studied in detail was moved on by individuals challenging the stasis of the class system. From the time of Elizabeth it was not the aristocrats that built the empire by 'filthy tradesmen', freebooters and pirates acting with "letters of marque" to pligh the high seas and trade.
The American colonies were lost due to the indolence and inertia of the traditional political system failing to respond to the need for political change.
By the time of the 19thC the class system was once again being challenged with the rise of left wing politics without which the huge social and political progressiveness of the 20thC would not have been possible.
Now contrast the sub continent of India, which was conquered by the Moghuls and then by the British, whilst they clung on the the most strict and unremitting system of class/caste hierarchy; static and counter progressive.
Mod note: This thread was split from viewtopic.php?f=5&t=15777 because it seems like a great topic and didn’t want Georgeanna’s thread to be overwhelmed