Three things: (1) Multiple territories or kingdoms, (2) centralized rule, (3) means of disciplining kingdoms (e.g. roads for transporting soldiers).
Sometimes education could be added to the list.
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a work in which the protagonist overcomes moderate difficulties.
what the empires that has ruled the world
The empires split up into smaller territories.
There are various characteristics of party de-alignment. They include breaking of ties between the parties involved, the electorate will abandon the affiliation with the other party and so much more.
Both empires shared similar laws and traditions.