Americans often assume that insurgency is a modern phenomenon, invented by Mao Zedong and refined by his emulators. The notion permeates official thinking, including Department of Defense definitions and doctrines. In reality, insurgency has existed ever since states and empires began attempting to impose their will on people too weak to resist with conventional military means. Indeed, counterinsurgency is a common function for most states and an inevitable one for empires.
That said, the strategic significance of insurgency has ebbed and flowed over time. When the chance of direct conflict between great powers was high, insurgency became background noise in the security system. But when direct conflict between the great powers was unlikely, insurgency assumed greater strategic significance. Since it was the only game in town, it often drew the attention of great powers as well as the weak or flawed states directly challenged by an insurgency-based opponent.
It is easy to see this pattern in the past 50 years of American history. Insurgency took on strategic significance at the beginning of the Cold War as nuclear weapons, U.S. military power and the creation of NATO lowered the probability of direct conflict with the Soviet Union, leading Moscow to sponsor insurgencies as an indirect means of weakening the West. Insurgency's strategic significance briefly ebbed following the American disengagement from Vietnam, but re-emerged as Soviet-backed insurgencies in Africa and the Americas seized state power or appeared ready to do so. With the demise of the Soviet Union and China's withdrawal from the business of sponsoring insurgencies, their strategic significance to the United States declined, only to explode again following the Sept. 11 attacks.