Which is a common tactic used in proxy wars? encouraging opposing powers’ citizens to emigrate sponsoring wars of liberation and revolutions controlling another country secretly buying weapons in preparation for domestic warfare

The correct answer is sponsoring wars of liberation and revolutions

For example, during the cold war, proxy wars were common between the Soviets and the United States. Since they couldn't fight each others, they decided to support opposing factions in other countries. For example, Afghanistan campaign where the Soviets tried to take the area was opposed by the Taliban locals who were supported by the United States. 

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