For the weak states, the cost of fighting back can be great. Sullivan's study shows that those lesser states suffer 81 percent of the battle deaths "when they choose to fight back against major power militaries."
If it's strictly a brute force confrontation, the major states will win 75 percent of the time, Sullivan says. But if a political settlement is also required, that number drops to 20 percent.
Surprisingly, the level of commitment "is only marginally statistically significant" in whether the major power wins or loses. In some cases, according to Sullivan's research, a higher commitment — as in a greater number of combat troops — actually "decreased the probability of success," possibly by making the smaller country more determined to win.
Sullivan draws a sharp contrast between the two Persian Gulf wars. The first war, Operation Desert Storm, "was a quick and decisive victory for the United States, and the allies suffered far fewer casualties than anyone had predicted," she writes.
"Instead of filling thousands of hospital beds in a protracted conflict, the United States liberated Kuwait after a six-week air campaign and a 100-hour ground war, losing only 146 soldiers in combat."
That success was so convincing that the then-chairman of the Joint Chiefs of Staff, Colin Powell, said the ghosts of Vietnam had been dispatched and the United States would immediately develop "the capability to prevail, quickly and cheaply, in any and all forms of conflict."
Then came Operation Iraqi Freedom. Hussein's regime collapsed, few American lives were lost, and the battle was declared over. Then the bottom fell out.
As Sullivan's study would predict, the effort to make Iraq into a democratic clone from the west has faltered, turning into a problem that "brute force" could not resolve.
So, where will it end? No one really knows, but after studying 122 wars, Sullivan has an opinion.
"I think that eventually, we will withdraw because more and more people think the price is too high," she said.