Military leaders frequently underestimate how big the wars they engage in will get.
Gen. Douglas MacArthur predicted U.S. troops could come home from the Korean War in time for Christmas, just months after the conflict started. But Chinese attacks that winter extended the war for years.
And President Donald Trump said in March that the Iran war would be a "short-term excursion," but it's now lasted more than five months with periods of escalation.
Research led by CU Boulder into how wars become more intense over time highlights the many risks of engaging in them. It also underscores why it's hard for anyone to predict their scope.
"War is inherently very unpredictable once it gets started," said Aaron Clauset , a professor of computer science at CU Boulder and the lead author of the statistical study. "The history of war and escalation indicates that any leader who claims that a war will be small is likely fooling both themselves and the public."
The study, published Aug. 5 in Science Advances , looked for patterns in the progression of civil and interstate wars, primarily from 1946 to 2008. It specifically used data on how many soldiers died in battle each year of a specific conflict to measure how wars escalated and de-escalated.
It found that while large civil wars tend to cool off over time, wars between nations "exhibit a persistent risk of continual escalation." It also found that escalation in war is "remarkably common."
"The data showed there's no systemic tendency for wars to get bigger or smaller," Clauset said. "Each additional year of fighting carries roughly a 10% chance of doubling in severity and about a 1% chance of increasing by 10 times."
Clauset said the analysis also shows that wars don't get big just because they last an especially long time. Ones that start with large death tolls also aren't necessarily destined to grow into larger conflicts.
Instead, Clauset said escalation dynamics, not a war's duration or initial intensity, is the primary mechanism that causes an armed conflict to grow to enormous sizes.
Ratcheting up
Unexpected things can happen during a war, like the entrance of a new ally or the expansion of a war to a new region. Such shifts can affect the decisions being made by each side.
Ceasefires and peace talks can also break down.
"When commitments become difficult to keep by either side in a conflict, wars tend to continue and drag on, and that's how escalation can ratchet up the intensity, which tends to further destabilize previous commitments," Clauset said.
The volatility caused by escalation shows how even a limited war with just two parties that starts with lower losses of life can grow into a much bigger one.
The study describes war as a volatile process "where violence can build and feed back on itself."
The research doesn't give policymakers a way to accurately forecast ongoing and future wars. But Clauset said it could still benefit presidents and policymakers who make wartime decisions.
"Our findings highlight the risks that all conflicts carry," he said. "The idea that war is uncertain is an old one. Our work shows that escalation risks further amplify that uncertainty, making it extremely difficult to forecast how large a war may ultimately become."
Forecasting the future
Clauset said research into why wars get big has been limited in the past because of challenges getting data from conflicts that ended decades ago.
Until more recently, it was hard to obtain centralized data of war deaths broken down by year.
The field is showing new potential, he said, thanks to new efforts to track the evolution of conflicts over time. And if researchers could someday get access to even more granular data from individual skirmishes, military decisions, and political negotiations, more could be learned about the evolution of war.
"The more granular the data available to scientists, the better we can likely understand how to prevent escalation from driving large wars," Clauset said.
