Answer:
The common denominator for such enormous empires as the Gupta Empire, or the Han Dynasty in China, who were so successful for a time in their countries, going as far as unifying them and transforming them into their current identities, is, that, throughout all the power they amassed and the riches, there was an undercurrent of corruption.
Because of the extensive sized of these empires, and the amount of power available, the emperors of these lands, regardless of how involved they might have been in government, were still only human, and could only control so much. In the end, corruption, the desire from those around the rulers to attain power and control of the empires, led to the downfall of most of them.
Even if these emperors were admired, and almost divinized by their people, at some point, the overreaching, the overextension, of their lands, made their power become thinner and thinner, and more vulnerable to the influence of those who became necessary to extend that power. Corruption then, was inevitable.
So I believe that one action that these emperors could have taken to prevent this from happening, would have been to not continue with their idea of land conquest, and imposition of their own views and traditions to lands that were different. Because these two conditions, to be maintained, required representatives, and military power. And those representatives, with power, became the very source of corruption that began to destroy the empires from the inside out.
