Why is an encirclement / flanking maneuver so disastrous for a defending military unit?

Question

Especially in a tactical sense (i.e. Napoleonic Warfare), not necessarily World War II grand strategy encirclement.

Answer 1

The damage is mainly psychological. The Greek phalanx was impregnable to frontal attack, look at Thermopyle and their advances in Persia under Alexander. But given a mobile assault as the Roman legions did, the Greeks were easily outdone. The phalanx was too unwieldy and could not turn to meet the flanking or rear attacks.

At Gettysburg, the South nearly rolled up the Union left flank and won the battle as they did at Chanclorsville. Even though the Union army was superior in numbers, the flanking movement left Joe Hooker a beaten man, the psychological factor beat him

Answer 2

You Asked
"Why is an encirclement / flanking maneuver so disastrous for a defending military unit? "

I am going to take "defending" as the operative word.

It can have several tactical implications that depend on the situation.

It suprises the enemy. They have to shift and defend a different area, or two or more areas at once and they may or may not be ready for that.

As stated above me you can cut off the defending unit from its supply lines, and lines of communication.

It can cause the enemy to have to defend multiple angles or sides instead of concentrating on just one area. This ultimately will decrease the amount of firepower they have to offer, and decrease their ability to react.

It can cause the enemy to have to redirect their men and material to defend the flanks, or areas that are being attacked, thereby decreasing their ability to defend their front.

Flanking also limits the enemys ability to manuver on you.

When you flank the enemy on both sides its called a "double envelopement."

You can attempt to encircle the enemy however Sun Tzu believed that encircled enemy's fight to the death, so you should leave atleast one escape route and just pick them off when they try to retreat.

Answer 3

It cuts off supply, logistics, reinforcements. Thus rendering the defending unit ineffective. That's encirclement, flanking allows you to roll up a defending unit from one side or another, while much of its assets are held in place by a portion of the attacking force. Basically making the defender fight on more than one front, or side.

Ummm, I believe it was allot more flanking in those times than encirclement, most of the warfare in Napoleonic times was terrain chosen very carefully by the defender or the attacker. Most winners than relied on sheer number and firepower due to the weapon ranges (Very Short) Body counts where staggering by today's standards.

Answer 4

a flanking maneuver is an assault on the enemy's flanks (the left or right wing of an army).it forces the enemy to draw off his central reserves to the assaulted area.as a result of this his centre gets weakened.once this is done a final frontal assault on the centre can do wonders for you and blunders for him!
a fine example of a battle where a flanking attack destroys the enemy is the french victory at austetlitz.
however when the flanks are well protected the attackers can face some tough opposition as in waterloo.