Le’ Notes #21: The Rubicon theory of war

This post discusses the Rubicon theory of war — where leaders fully commit to war after crossing the Rubicon River as Caesar did.

In role-playing games, it’s known as the “point of no return“, where you can no longer save your progress and have to fully commit to battling the game’s final boss, either in sequence like Kefka’s epic finale in Final Fantasy VI or alone, like Izanami no Ookami’s true ending battle in Persona 4. The fact that you can no longer save or go back to finish your unfinished business in the game world triggers this mindset that sorta goes “Since I can’t go back, might as well get this over with”.

The more technical term for this shift in mindset is known as the shift from a deliberative mindset to an implemental one. As Johnson and Tierney [PDF] describe it, the shift occurs when leaders are faced with a proverbial Rubicon River. To be precise, the theory refers to Caesar’s crossing of the Rubicon River in 49 BC. There was an ancient Roman law that specifically forbade a general to cross the Rubicon with an army into Italy. To do so was treason. Faced with this, Caesar crossed the Rubicon, marking his wholehearted commitment to starting a civil war and being branded a traitor. That’s where the theory’s name comes from.

Johnson and Tierney posit that when leaders are faced with a proverbial Rubicon River, i.e. a specific critical juncture in events that they must commit to see until the very end (of course, this also includes perceived importance of the event), they stop deliberating and begin implementing their actions. Mostly by going to war. It can also be said that when the prospect of war seems highly likely, leaders are going to commit to war and disregard other alternatives that might pop up since the army has already been set into motion. The shift from deliberative to implemental is often characterised by increasingly hawkish behaviour, risky (even reckless) military planning, an elevated perception of victory, rejection of new information which may contradict their end goal, selective processing of new information, vulnerability to confirmation bias and self-serving evaluations.

All of this relates back to one particular cognitive bias: the overconfidence bias. This is the central argument of Johnson and Tierney, who posit that increases in overconfidence translate into increasing probability of war. For a more scientific approach to the subject of overconfidence and underconfidence, see Moore and Cain [paywall].


In World War I, this was visible in the July Crisis of 1914. However, one could also argue that the perceived destabilisation of Europe was evident from the Anglo-German arms race from 1898-1912 and the subsequent crises, such as the 1905 Moroccan crisis and 1912 Balkan wars. The assassination of Franz Ferdinand can be considered the culmination of these tensions among European powers, the tipping point where European powers finally decided to “cross the Rubicon” and perceive conflict as imminent. Across Europe and even in the United States, decision-makers who were at first reluctant to go to war ended up going to war based on this perception: they were confident that their armies would win. They were even more confident when they believed the war was going to be a short one, that they would be home by Christmas [Hallifax, 2010, paywall]. They were wrong.

However, to be balanced, Johnson and Tierney seem to favour the pessimistic tendencies of overconfidence in war. A degree of confidence is beneficial in war. Even Clausewitz would agree, given that we associate “boldness” with “confidence”. However, the same Clausewitz would also advocate for not being overconfident and learn to harness the creative power of boldness with a “reflective mind”.

Let us admit that boldness in war even has its own prerogatives. It must be granted a certain power over and above successful calculations involving space, time, and magnitude of forces, for wherever it is superior, it will take advantage of its opponent’s weakness.

The higher up the chain of command, the greater is the need for boldness to be supported by a reflective mind, so that boldness does not degenerate into purposeless bursts of blind passion.

– Clausewitz, On War, Book III, chapter 6

Does that mean overconfidence might be beneficial in deciding to go to war? In Overconfidence and War [book], Johnson argues that overconfidence is “adaptive”, in a sense that it is favoured by natural selection and thus, prevalent in human psychology. From an evolutionary perspective, overconfidence would confer benefits such as increased gain from risks rather than dwelling on missed opportunities and an increased performance in conflict due to suppression of disadvantageous thoughts. If such was the case, then there is a possibility that overconfidence might also play a role in preparations for war and boosting wartime conduct.

Furthermore, Johnson also accounts for the potential occurrence of group-think in influencing war decisions. Overconfidence might not just be prevalent in the individual, rather, it could be present, even magnified, when in groups. This is important, considering that war decisions are not made by individuals, but a group of people.

In summary, the overconfidence bias represented by the Rubicon theory of war adds on the multitude of psychological explanations of war and fundamentally builds on the existing rational-choice theory. It accounts for uncertainty, which is an eternal inherent feature in war, in the decision-making process. Most importantly, the overconfidence explanation also factors in group dynamics that can work to reinforce existing biases. This perhaps is the most important contribution due to the fact that war decisions are often not made by individuals acting as (presumably) rational and monolithic actors, but rather by groups of people that interact according to group dynamics.

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