When planning for a mission someone somewhere works out the math on expected casualties. Usually this is the S1 and S4 trying to figure out how many replacements they will need and how much medical support the unit will need during different phases of the operation. These numbers come out of the calculator either as a percentage of the unit, or as an estimated digit.
We can look at the numbers for American and VC dead in Vietnam to get a good feel for historical "counterinsurgency" ops. Round the VC death to 1 million and American to 58,000 and we see that the technological advantage of air power and artillery really helps. In Afghanistan the Soviets were even more successful than the Americans in Vietnam, roughly 1 million Afghans dead to under 14,000 Soviet soldiers.
So what does this tell us? A foreign power with a technical advantage will really whoop up on an insurgent.
When we look at a different type of war, such as the American Civil War, where there was not a technical advantage by either side, we see massive casualties.
The insurgencies that work are the ones that nullify the government advantages. The will of the people is what wins an insurgency, not military might (the .gov always has more military might). Fighting the government with bullets is not as effective as winning the hearts and minds of the populace. When the people see the insurgent as a better alternative than the .gov even if the .gov bends to appease the people the insurgent will have achieved success.
Case in point Egypt and Libya. Not a lot of bullets flew in Egypt, the insurgents had the support of the people. In Libya the insurgents do not have enough support to keep the .gov from cracking down with bullets. So, to minimize casualties insurgents must fight for the hearts and minds first and foremost.