Defeat in detail, or divide and conquer, is a military tactic of bringing a large portion of one's own force to bear on small enemy units in sequence, rather than engaging the bulk of the enemy force all at once. This exposes one's own units to many small risks but allows for the eventual destruction of an entire enemy force.
Use
In military strategy and tactics, a recurring theme is that units are strengthened by proximity to supporting units. Nearby units can fire on an attacker's flank, lend indirect fire support such as artillery or maneuver to counterattack. Defeat in detail is the tactic of exploiting failures of an enemy force to co-ordinate and support the various smaller units that make up the force. An overwhelming attack on one defending subunit minimizes casualties on the attacking side and can be repeated a number of times against the defending subunits until all are eliminated. An attacker can successfully conduct the tactic of defeat in detail by exploiting the absolute weaknesses or the comparative disadvantages in the deployment or structure of defending troops, or advantages, such as maneuvering speed, that the defender cannot match. In an asymmetric support structure, A can support B but unit B cannot support unit A. For example, during World War I, when horse cavalry were still in use to some extent, aircraft could support cavalry, but cavalry had little or no ability to support aircraft. Thus, if a unit is equally suited for use against cavalry and against aircraft, using it to eliminate enemy aircraft would have benefits that would last well into future engagements against enemy cavalry units weaker for their lack of support, but using it against enemy cavalry, leaving the enemy aircraft intact for subsequent engagements, would bring benefits during that engagement alone.
Weaknesses of defenders
Dug-in units that are spread out over so wide a distance that the maximum effective range of their weapons is significantly shorter than the distance between units, which prevents those units from supporting the flanks of neighboring units.
Defending units on opposite sides of physical barriers such as hills, forests or rivers.
Defending units whose artillery support is too far to the rear and so cannot effectively engage attackers.
Defending units that have no effective communications with their command structure and so cannot request assistance.
Enabling methods
The following methods can enable the attacker to defeat the enemy in detail:
Attacking one unit faster than other defending units can move to counter-attack.
Attacking faster than the defending intelligence, communications, command or control systems can respond to.
Disabling or disrupting systems required for one defending unit to support another.
1862: Stonewall Jackson's Shenandoah Valley campaign, in which Jackson defeated three Union commands with his own command, by fighting each of the enemy columns in turn while the Union commands were separated from each other by impassable terrain or a significant distance.
1941: Operation Compass, when the British defeated an Italian force more than four times larger in North Africa by exploiting the fact that the Italian defenses could not support each other.
