Until the seventeenth century, a war was essentially a war between one mass and another mass. For his part, Boulainvilliers makes the relationship of war part of every social relationship, subdivides it into thousands of different channels, and reveals war to be a sort of permanent state that exists between groups, fronts, and tactical units as they in some sense civilize one another, come into conflict with one another, or on the contrary, form alliances. There are no more multiple and stable great masses, but there is a multiple war. In one sense, it is a war of every man against every man, but it obviously not a war of every man against every man in the abstract an — I think — unreal sense in which Hobbes spoke of the war of every man against every man when he tried to demonstrate that it is not the war of every man against every man that is at work in the social body. With Boulainvilliers, in contrast, we have a generalized war that permeates the entire social body and the entire history of the social body; it is obviously not the sort of war in which individuals fight individuals, but one in which groups fight groups.
war turns the very disruption of right into a grid of intelligibility, and makes it possible to determine the force relationship that always underpins a certain relationship of right. Boulainvilliers can thus integrate events such as wars, invasions, and change — which were once seen simply as naked acts of violence — into a whole layer of contents and prophecies that covered society in its entirety (because, as we have seen, they affect right, the economy, taxation, religion, beliefs, education, the study of languages, and juridical institutions). A history that takes as its starting point the fact of war itself and makes its analysis in terms of war can relate all these things — war, religion, politics, manners, and characters — and can therefore act as a principle that allows us to understand history. According to Boulainvilliers, it is war that makes society intelligible, and I think that the same can be said of all historical discourse. 
The other thing I would like to stress is that by making the force relationship intervene as a sort of war that is constantly going on within society, Boulainvilliers was able to recuperate — this time in historical terms — the whole kind of analysis that we find in Machiavelli. But for Machiavelli, the relationship of force was essentially described as a political technique that had to be put in the hands of the sovereign. The relationship of force now becomes a historical object that someone other than the sovereign – something like a nation (like the aristocracy or, at a later stage, the bourgeoisie) — can locate and determine within its own history. The relationship of force, which was once an essentially a political object, becomes a historical object, or rather a historico-political object, because it is by analyzing this relationship of force that the nobility, for example, can acquire a new self-awareness, recover its knowledge, and once more become a political force within the field of political forces.
war is basically historical discourse’s truth-matrix. “Historical discourse’s truth-matrix” means this: What philosophy or right would have us believe notwithstanding, truth does not begin, or truth and the Logos do not begin, when violence ceases. On the contrary, it began when the nobility started to wage its political war against both the Third Estate and the monarchy, and it was in this war and by thinking of history in terms of war that something resembling what we now know as historical discourse could establish itself.
One last remark, finally. The reason Clausewitz could say one day…that war was the continuation of politics by other means is that, in the seventeenth century…someone was able to analyze politics, talk about politics, and demonstrate that politics is the continuation of war by other means.
–Foucault, Society Must Be Defended, p162-5 [bolding my own]
 Snipped and footnoted by me: When I speak of grid of intelligibility, I am obviously not saying that what Boulainvilliers said is true. One could probably even demonstrated that everything he said was false. I am simply saying that it could be demonstrated. What was said in the seventeens century about the Trojan origins of the Franks, or about how they emigrated and left France under the leadership of a certain Sigovège at some point and then returned, cannot be said to have anything to do with our regime of truth and error. In our terms, it is neither true nor false. The grid of intelligibility established by Boulainvillers, in contrast, does, I think, establish a certain regime, a certain division between truth and error, that can be applied to Boulainvilliers’s own discourse and that can say that his discourse is wrong – wrong as a whole and wrong about the details. Even that it is all wrong, if you like. The fact remains that it is this grid of intelligibility that has been established from our historical discourse.