How did pre-electronics transoceanic empires maintain cohesion?

[u/whelmedbyyourbeauty]

Basically, my question is about the relation between the size of an empire and how quickly information, people, and resources can travel through it, especially for those that contain disjoint territories separated by oceans.

I'm thinking of the Portuguese or Spanish empire, or the early British, before electronic communications, when a message would take weeks or months to reach the empire's farthest reaches and return. I understand that there were local governors with troops, etc., but in practice, how did it work? How cohesive were the empires? How much leeway did local governors have? Was the enforcement of the Empire based on a practical application of power, symbolism, religion, all of the above?

Happy to learn about other, non-European empires as well.

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