Not a whole lot of analytical work has been done on third-party insurgencies. A third-party insurgency is a conflict where an external state or trans-national organization played a major role in initiating, sustaining, bringing to victory, or otherwise supporting a rebellion or insurgency. Kind of like what is going on in Donetsk and Lugansk in Ukraine.
We did do a little work to examine if the level of outside support results in insurgent victory. It was been the perception of the number of counterinsurgent theorists that significant outside support is important for an insurgent victory. Our analysis, based upon an examination of 89 cases was that it was in fact, not a primary driver of insurgent success. To provide a table from page 79 of America’s Modern Wars:
| Outcome by Type of Outside Support | |||||
| Outcome | Primarily Indigenous | Some | Considerable | Not Applicable | Total |
| Blue | 11 | 20 | 9 | 2 | 42 |
| Gray | 5 | 6 | 0 | 0 | 11 |
| Red | 7 | 18 | 5 | 0 | 30 |
| Total | 23 | 44 | 14 | 2 | 83 |
This table compares the amount of outside support (primarily indigenous, some, and considerable) to the outcome (blue = counterinsurgent victory, red = insurgency victory, and gray = outcome is not a clear victory for either side). Outcome compared to type of outside support produced no discernable pattern. The counterinsurgents or intervening force tended to win more often then not, no matter what the degree of outside support was for the insurgency. Our statistical test indicated that there was no correlation here.
There was no correlation whether we tested to our entire dataset of 83 cases, limited the test to only those 62 cases that were clearly insurgencies (did not include the peacekeeping operations and interventions in our larger dataset), or only those 36 case that were insurgencies against outside intervening forces. If there was a consistent trend in this data, it was that insurgencies with considerable outside support lost more often than insurgencies that were primarily indigenous. This is counterintuitive, but it made of cases that include almost every major and not-so-major insurgency since World War II. But there appears to be little correlation between the degree of outside support for an insurgency and the outcome of the insurgency.
Of course, the purpose of the third-party insurgency may not be to obtain clear victory, but for lesser political purposes, including disrupting an opponent or forcing concessions from them.
