While the two Empires were facing Confronting_problem enormous internal difficulties , the Serbs took Creating the favorable opportunity to expand Expansion its domain .

Catherine the Great of Russia took advantage of the disorder to consolidate her control over the weak polities of the Caucasus , which was , for swaths of it , an integral Persian domain .

Starting Process_start from Emperor Wu 's reign ( r. 141–87 BC ) , the Han empire changed Change from a relatively passive foreign policy to an offensive strategy to deal Resolve_problem with the increasing Xiongnu incursions on the northern frontier and also according to general imperial policy to expand Expansion the domain .