In the 60s, my father wrote a small but enormously influential book called The Principles of War. In it, he applied the principles of physical warfare to what he called strategic evangelism. This idea of warfare is necessary in order to understand a central part of what is happening here, and by this I mean the concept of the decisive point. A decisive point is one which is simultaneously strategic and feasible. Strategic means that it would be a significant loss to the enemy if taken. Feasible means that it is possible to take. New York City is strategic but not feasible. Bovill is feasible but not strategic. But small towns with major universities (Moscow and Pullman, say) are both. Douglas Wilson

Jim Wilson is giving away The Principles of War on his website; here’s a safe link. He uses the phrase “decisive point” a few times:

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Whether the offensive is directed against the whole front or against one segment of the enemy army,

In either case it should be well understood that there is in every battlefield a decisive point, the possession of which, more than any other, helps to secure the victory by enabling its holder to make proper application of the Principles of War. Arrangements should therefore be made for striking the Decisive blow upon this point (Jomini).

There are two things that determine a decisive point. The first is the relative importance of that point compared to the rest of the front. The second is the feasibility of taking that point. If it is not important, it is not decisive. If it is important but not feasible to take, then it is not decisive. This is very important. Be alert for teaching on the decisive point in succeeding chapters.

Whether the offense is made along the whole front or at a decisive point, it has several basic characteristics. In attitude it is bold; in direction it is forward toward the enemy at the objective; as its means it uses effective weapons. . . . (Jim Wilson, Principles of War [Moscow, ID: Community Christian Ministries, 1991], 26–27)

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Concentration also plays a vital part in mass evangelism. In the chapter “Offensive” it was brought out that when the army on the offense does not possess an overwhelming superiority it is not feasible to launch an attack along the whole front to take the objective. In such a case a decisive point must be selected against which to strike a decisive blow. An overwhelming superiority must be gained at the chosen point. This superiority is obtained by transferring forces from the rest of the line to the decisive point. This weakens the rest of the line, but enough should be left in order to keep the enemy occupied. Even if minor defeats occur along the weakened portion, this is not crucial, because in the meantime you have served the decisive blow at the decisive point that defeats the enemy.

An excellent example of this is found in Montgomery’s preparations for the first battle of El Alamein. In his own words:

Then from the bits and pieces in Egypt I was going to form a new corps, the 10th Corps, strong in armour; this would never hold the line but would be to us what the Afrika Korps was to Rommel; the formation of this new 10^th Corps had already begun.

Montgomery concluded that Rommel would make his main effort on the south or inland flank. This was the Alam Halfa Ridge. Since Montgomery weakened his northern flank in order to concentrate on Alam Halfa, he strengthened it with mine fields and wire so it could be held with a minimum of troops. At Alam Halfa, the decisive point, he concentrated two mobile armored divisions, the 44^th Infantry Division, and his newly formed armored division of 400 tanks dug in behind a screen of six-pounder anti-tank guns. From August 31 to September 6, 1942, the Afrika Korps pounded against this line, all the while being hit hard by the mobile and dug-in tanks and by the British Desert Air Force. Rommel retreated on the 6^th with a decimated Afrika Korps. He had been defeated, and Montgomery had won a decisive victory. Thus, concentration achieved the turning point of the war in Africa. . . . (Ibid., 44–46)

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Economy of force is efficiency in fighting, effectiveness in warfare. If our objective is the annihilation of the enemy army, we will take the offensive at the decisive point. In order to do this effectively, the combined application of all principles of war is necessary. This statement by General Erfurth mentions or implies most of the principles of war:

To concentrate overwhelmingly superior members at the decisive points is impossible without strategic surprise. The assembly of the shock-group must be done as quickly as possible in such a way that all units can attack at one and the same time.

Each of the following principles, when applied separately, economizes force. When they are applied in unison, economy of force is achieved. Let us look at each principle in the light of economy of force, realizing that all of them are interdependent:

1. Objective: The greatest incentive for economizing is to know where you are going and then go there.

2. Offense: “Going” economizes forces. It takes less force to mount an offense against one point than to defend all points.

3. Security: If the enemy does not know what we are going to do, we can do it with less force. If he knows, he will then be prepared and we may not be able to do it at all, even with much greater force.

4. Surprise: This principle certainly allows a commander to do the job with less force.

5. Mobility: Mobility economizes force by increasing, in effect, the numbers of men and arms.
   

   A leader who aims at mobility should not be afraid to strain his troops to the limit in order that they may reach the battlefield in time. Many victories were made possible by forced marches. Mobility equals increase in numbers (Erfurth).

6. Cooperation: When allied forces advance with a common objective and in unity, they can attain victory with fewer men than if they had acted independently.

7. Concentration: This may seem to be, but is not, the opposite of economy of force. To use one’s force in driblets here and there may only result in consistent defeat. But if we concentrate at the decisive points, we are using economy of force.

There is such a thing as over-concentration in places that are not decisive points. “Consequently, the fronts where no decisions are being sought should be manned with a minimum of force” (Erfurth). To concentrate at nondecisive points violates economy of force. It is better to have one’s force scattered in driblets at decisive points than to have it concentrated at a nondecisive point.

As we apply the various aspects of the principle of economy of force to the spiritual war in which we are engaged, we can say that any concentration of Christians where there are few or no non-Christians is an overconcentration at a point that is not decisive. To have a concentration of Christians where paganism is thick and rampant is compatible with the principles of war.

Because Christians have a tendency to concentrate at nondecisive points, it may be difficult to get more than a few away from places of mislocated concentration to points where decisive battles are being fought. The few may not be enough for effective concentration, but their proper deployment is a step in the right direction, a step toward economy of force. Not to send a few to the decisive points would violate several principles of war. Economy of force uses what is available to do the job. (Ibid., 112–115)

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Carl Gustaf Emil Mannerheim greets Adolf Hitler alongside General Waldemar Erfurth (right), quoted above, in Finland.