The intuition behind the maxim divide et impera is clear. Â If they’re busy fighting each other, they not fighting you. Â And that’s obviously in your interest (assuming, that is, you are some sort of occupier or metropole seeking to extract rents from a local population.) Â Devious and underhanded? Â Sure. Â Morally repugnant? Â If you’re inclined to view politics through such a lens. Â But effective? Â Self-evidently.
Or so you might think.
Brenton Kenkel, a University of Rochester doctoral student currently on fellowship at Princeton, argues otherwise in this fascinating working paper.
To evaluate the logic behind divide and conquer, Brenton analyzes a game-theoretic model wherein a conqueror demands tribute from a population consisting of an arbitrary number of groups, each of which chooses how much effort to devote to economically productive activity, resistance against the conqueror, and conflict with other groups.  He derives a number of interesting results, most of which I’ll briefly discuss, but the basic argument is straightforward—the more time groups spend fighting each other, the less time they spend fighting the conqueror, which means a larger share of the total resources can be demanded; but time spent fighting anyone is time that isn’t spent on economically productive activities, and so there’s less available to demand.  Fostering internal conflict ensures that the conqueror gets a larger slice of a smaller pie.  And while you might think that means the net effect is ambiguous, Brenton’s model indicates that the latter effect always trumps the former.
That’s not to say that fostering internal conflict is never optimal. Â Conditional on there being pre-existing divisions in society, it is better to turn the groups against one another. Â But that doesn’t quite validate the logic of divide and conquer, because Brenton further shows that the conqueror is generally better off if population is unified than if they are divided. Â As he aptly puts it, divide and conquer is a second best strategy—an optimal response to a situation the conqueror would just as soon alter if at all possible.
In other words, whether it pays to divide and conquer depends on what you think that strategy entails.  According to the ultimate arbiter of everything on the internet, Wikipedia, “elements of this technique involve:
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creating or encouraging divisions among the subjects to prevent alliances that could challenge the sovereign
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aiding and promoting those who are willing to cooperate with the sovereign
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fostering distrust and enmity between local rulers
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encouraging meaningless expenditures that reduce the capability for political and military spending.”
Brenton’s analysis indicates that conquerors do not generally have an incentive to create or encourage divisions among the population. Â They often have an incentive to ruthlessly exploit those divisions that already exist, but that doesn’t mean they profit from creating new divisions.
Yet his paper does indeed indicate that it can be beneficial to promote some groups over others, as one would expect.  As an example, he points to China’s effort to increase the Han population in the Xinjiang province.  This has had the effect of reducing violence against the Chinese government—at least in part because it has reduced the attractiveness of independence to the Uyghurs by reducing their ability to dominate a new state—as well as increasing economic productivity.
There is one condition under which conquerors potentially do prefer the population to be fragmented—when no group is particularly productive and there is abundant natural resource wealth. Â In such cases, the fact that intergroup conflict not only siphons away resistance but also economic productivity has little impact on the size of the pie. Â This may explain, for example, why colonial powers adopted different policies in different places, and why the legacy of colonialism differs so widely across the world. Â But this is the exception that proves the rule. Â It is important to consider not just who has the upper hand in whatever military engagements take place, but how much value is destroyed (or not created) by said violence.
Note that this is a work in progress.  Brenton would welcome any comments you might have.  His email address is bkenkel<at>princeton.edu.
I’ve written a few things on divide-and-rule and divide-and-conquer logics :-). In general, unite-and-rule strategies make sense *if* the ruler expects loyalty from the group. If not, then the process of uniting-and-ruling provides vectors for more dangerous resistance. I’ll take a look at the working paper when able, but I should also note that there are *significantly* different ways of implementing divide-and-rule policies.
Excellent point, Dan. I’ll look at your work on this, and encourage Brenton to do so as well.
this is pretty cool
I have not read the paper but I have read the first sentence, which is:
“Violent political conflict often ends—or begins—with a piece of territory coming under the rule of an outside power.”
Hmm. When was the last time an outside power — call it state X — invaded a piece of territory outside its generally recognized boundaries with the intention of permanently annexing or otherwise incorporating that territory? Maybe Iraq’s invasion of Kuwait in ’90? Maybe, arguably, Israel’s de facto annexation of the West Bank in ’67? Maybe India’s seizure of Goa from Portugal in ’61? Maybe China’s invasion of Tibet in, what was it, 1950? Perhaps some episodes from the Balkan wars of the ’90s qualify (but I’m rather doubtful).
There are lots of examples of secession or attempted secession one can think of, but not v. many examples of territorial conquest in the last 60 or so years. So the word “often” in the first sentence strikes me as quite wrong. Why is territorial conquest rare today? Well, for one thing it’s no longer considered a legitimate activity, as it was for much of the state system’s history.
K.J. Holsti has written:
“The de-legitimization of conquest, both as a right of sovereignty and as a norm of international law, is in my view the most important change in the international system since the early days of the states system in the seventeenth century…. The institution of sovereignty and the universal norm of self-government are powerful underpinnings for the obsolescence of conquest. If there is any single candidate for the claim that ‘everything has changed,’ the obsolescence of conquest is my choice.”
Taming the Sovereigns: Institutional Change in International Politics (Cambridge Univ Press, 2004), p.320
You’re right that we rarely see conquest anymore. Perhaps Brenton should have said “has often”, using the past tense, but, as he discusses in the first footnote, he speaks of conquest primarily for ease of exposition. His argument applies just as well to relations between central governments and secessionist regions. Besides, the “permanent annexation” qualifier is all yours. All Brenton said was “with a piece of territory coming under the rule of an outside power”, which we’ve seen in Iraq and Afghanistan. The dynamics he describes in the paper are just as relevant to short-term nation-building efforts as they are permanent annexations.
Incidentally, as I’ve mentioned before, though the decline of conquest is indisputable, the causes thereof are less clear. Even in the absence of norms and international law, we’d expected a decline in conquest for economic and technological reasons. (See here https://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8286035 .) You’re welcome to keep reminding me that some people believe that a combination of norms and international law explain the decline of conquest, but if you’re not going to address the argument I’ve repeatedly made–that the phenomenon of interest is overdetermined–I’m not sure what good that’s doing either of us.
I take the point re the dynamics applying to short-term ‘nation building’ efforts, at least I suppose in a case like the Provisional Coalition Authority in Iraq. I was reacting entirely to the first sentence, as I said, where I do think the past tense would be an improvement. The first sentence of a piece does tend to set the tone and throwing in a footnote saying that the word “conquest” is used for ease of exposition I’m not sure is enough to avoid putting off some people who might otherwise read the paper.
“Even in the absence of norms and international law, we’d expected a decline in conquest for economic and technological reasons.”
This does sound sort of familiar, yes, but I don’t recall your having said it ‘repeatedly’. However, I’ll assume my recollection is to blame here. I will follow the link, which I haven’t done yet.
Fair enough, on both points.
A brief comment on one statement by Gartzke & Rohner:
https://howlatpluto.blogspot.com/2013/09/note-on-norm-enforcement.html
Machiavelli had a fair deal to say about the wisdom of divide and rule strategies (not a fan). Check out Prince XX (if I remember correctly) and the Discourses somewhere toward the end of book III for some interesting advice countering the conventional wisdom in ways that parallel Kenkel’s argument but also discusses other problems in holding divided societies (especially the external vulnerabilities it might create).