The tool itself is not evil; the intention of the person working with the tool determines its use.
The United States Military, over the past half century, has been designed to defeat enemy combat formations as its primary goal, not to defeat them and then maintain the land captured on the field of battle.
When the Continental Congress declared independence of the United Kingdom on July 4, 1776 in the name of the 13 states, the formation of a national standing army was not foremost goal that was envisioned for the nation. The state militias were the primary offensive / defensive forces the founding fathers thought would be used to win the freedom. This, however, quickly proved false due to the nature of militias, and the type of campaign that was required to be fought to defeat the British.
The Continental Army under direct command of General George Washington never won a set piece battle against the British till 1781. Other commanders did win battles, but the goal of General Washington was to just keep the American Army in the field to thwart the British. Controlling parts of the local land with enough forces to ensure that the British would have to maintain proportionally more forces against him, thereby allowing other smaller armies to fight and win battles of their choosing against the now spread out British.
The standing army swelled in the summer, shrunk in the winter on a routine basis. After the Treaty of Paris in 1783, the standing army and navy shrank down to below what was needed even to defend against pirates.
The War of 1812 saw the army again go up in strength during the war, then it shrunk down again afterwards but not to the same level as before. As the nation expanded the core size of the military forces slowly grew in size matching the new military needs.
The Mexican War saw the expansion of the army to handle the war but the nature of war had slightly changed. Not only was defeating of the enemy required, but the roads over which supplies had to traverse also had to be maintained under military control. Prior wars in the US the land was always friendly, and the need to station troops along the way was not required. As battles moved into initially foreign controlled lands the ratio of front line troops to rear area troops started to enlarge. The logistics train required troops to remain behind the front lines to guard the supplies line as well as send supplies to the battle front.
This expansion of rear area garrisons and supply depot oriented troops when compared against front line troops can easily be seen during the US Civil War of 1861-1865. The US was not the only nation adjusting the number of troops needed behind the lines. British, French, Germany, Russian. Japanese powers also started to require larger standing armies to perform the same function as technology allowed less people on the front line, while shifting more people behind the line to keep those in front supplied.
The up and down sizing of the US military has occurred during every conflict.
The Korean war of 1950-1953 saw the last time that the US fielded an army that was designed to both fight the enemy and hold the land won. The fact that it retreated so many times during the war was mainly a function of the politics involved which limited the number of men deployed over what was needed to win. This was done by substituting technology — aircraft — as a "force amplifier" to make up for the artificial limit imposed on the number of ground forces deployed.
The end of the Korean war saw a slight reduction of military strength in raw numbers. A military philosophy change that was rapidly implemented was to substitute even more technology for people regardless if it was valid in order to have more firepower per person on the front line. This was not anything new, but the scope of replacement being proposed and how it was implemented was beyond what had been done before.
To fight the enemy fire bases were set up — think of them as Medieval castles — to control the surrounding land. The big difference is that in Medieval times the castles were built every 20 miles throughout the whole land and was actively monitored and patrolled. The people in the castle, though at times mean and cruel to those they governed, needed those people in order to stay in power and to earn money. In Vietnam fire bases were set up, isolated, abandoned, re-occupied time and again and the military people — USA politicians — had no real direct interest in the land nor the people.
The new way of fighting was to bring more firepower to the front line was by the use of helicopters, even more air power, and automatic rifle weapons to put more bullets toward the enemy. The helicopters were there to move troops to where the enemy was. Instead of having lots of troops and have a solid line and move toward the enemy, it was to use helicopters to move the troops to the enemy and then use air power in support. The unit was no longer self supported with friendlies directly behind. It became necessary that ANY force deployed required air power in order to survive. In of itself, a unit could not engage any enemy on the field and in a sustained fight prevail without air (and artillery when in range) support.
A direct effect of using troops in this manner was that the military was always reacting to where the enemy was at. When lots of combat erupted some units had to be left unsupported by air or artillery. This was built into the system by design. No unit could sustain combat on its own due to the political / military doctrine of having less people in the ground combat forces and using air power as a substitute for them to win individual battles.
The policy of having widely scattered fire bases with patrols going out into the field, meant that since the land was never really occupied, the same land was fought over time and again, and the enemy was able to choose when to fight.
The end of the Vietnam War the politicians again shrank the military down to a lower level. However, with the Warsaw Pack intact sustained by the backing by the Soviet Union, the military had to give up troops on the ground yet again and still had to have enough troops to deter Soviet forces from any attack. They did this by presenting a strong "attack" force using armor and aircraft that the Eastern Block would have to fight and destroy quickly. This force was built such that it would have a high probability of defeating any Eastern Block attack and thus deter them from attacking.
When President Carter was elected in 1976, part of his philosophy was to shrink the military in raw numbers to appease promises and to pay for social programs, but allow the military to accomplish the same military goal. The only way to accomplish this was to strengthen the firepower of the military units.
Under President Carter spending increased dramatically — for hardware not for people.
As the number of people in the military went down, an increased amount firepower and air power has to occur to compensate for the loss of physical troop strength. This forced the military and congress to fund research and weapons to increase the firepower and make all units more of a heavy armor unit in order to defeat the enemy ground forces. Money now had to be spent to create new weapons, produce them, and maintain them. For the industrialists, which the Republicans have traditionally represented over the past 100 years, this means long term profits. For the overall business community this is only valid if the items being purchased are replaced every 10 years - or upgraded / improved every so many years to maintain the profits. As the numbers of people using equipment goes down, the cost to produce each item, however, goes up.
The Democrats liked this plan since in raw numbers the military DOES shrink. This caters to their most vocal supporters. It also means, indirectly, that the U.S. has to be more selective as to where it gets involved due to the sheer lack of combat troops to send and so the liberal view of avoiding combat is accomplished regardless of which party is in power.
The shrinking number of people in the various military branches of arms meant that there could no longer be any "spare" regular infantry divisions around. To allow more to be done with less this meant shifting of even more firepower to aviation units ("assets" in militarese) in order for the ground forces to prevail against an enemy combat formation.
This concentration of firepower into specialized divisions and supplementing them with air support, means that that when an enemy force is defeated on the ground there are no units behind the front line to hold the ground since every unit is on the front line. It also means there are not even divisions to guard the flanks of the attack units. Every unit is on their own.
As seen in Vietnam when a unit is on its own it cannot win a sustained battle without air support. It is not designed to fight without it.
An example of this downgrading of combat formations and supplementing them with air assets is the shrinking of Marine infantry platoon. It has gone from 4 squads, with 12 men with a squad leader plus a platoon leader, to 3 squads of 13 people each in a Marine platoon. While this reduction in numbers should mean a 25% loss of firepower, increasing the per person firepower with light machine guns (M60s), and varied automatic weapons only causes a loss of around 10% in firepower (This is very similar to what the Germans did in 1942 when they reorganized their rifle divisions.) However, just like Germany combat formations of WWII, when you start to lose troops and do not have the external fire support behind these troops, then there are not enough people on the ground to attack or hold the ground they have.
The Gulf War of 1990-1991 was a battle perfect for the US military. A limited goal: remove Iraqi forces from Kuwait.
The land war only lasted 100 hours which meant attacking units were never out of direct support of rear area units. They were all within a few hundred miles of their jump off bases which were all in friendly land. The land that was captured from Iraq was not laced with populated centers. As such there was no need for rear area troops. This masked the limitations of the force structure (TOE) that the Army operates under.
The military that deployed to the Middle East in 2002 was smaller but with even more firepower per person than the 1990 version. This firepower base was in the up-gunned tanks and air units not the in the number of personnel in ground units. This force had the same orders as before: defeat the Iraqi military. The orders did not include holding land behind them, nor even their flanks. It was to attack and destroy enemy forces.
This is a flaw in any modern military planning when you have no plans to control the land captured. This is a direct result of the 1960s era idea of fire bases, air power, and random patrols to control the land thinking all the people want you there.
The reduction of the military to an "attack only" force eliminates garrison and flank units.
During the Second World War as Allied (or Axis) captured land they placed garrison troops in towns, roads, bridges, everywhere they could. Not in every village troops were stationed, but they always had troops close enough to search for downed fliers, visit villages, walk the roads etc all the time. The constant presence made any resistance work difficult and dangerous. For the Allies MPs were always in all villages and towns that supplies came through and along the roads. Once into Germany and Italy they maintained forces everywhere to ensure control. It was part of the whole combat plan on how quickly troops got into every population center.
In combat operations every division was involved in assaults but not every one lead the attack, many were flank divisions that followed alongside the main attack during the advance. This was missing in the Gulf Wars: every division was leading its own attack. There were not any support infantry flank units by design.
The attack through the desert by armored units is a classic one lifted from the likes of Rommel and Wavell. However, like them, it only works if the supplies can follow them. Most supply units do not have tracked vehicles to cross sand and instead must stay on roads or known hard land.
The armored assault to Baghdad the US command used standard "Blitzkrieg" tactics of bypassing well defended locations that did not block their drive to Baghdad. Unlike the 2nd World War, there were no units to ensure that the bypassed units could not strike out. As a result, if the bypassed Iraqis had better coordination and independent aggressiveness, they could have easily cut the US supply routes since there were never any units guarding any roads. In the middle of the night they could have even walked out for two hours, planted mines on the roads and walked back into the bypassed towns and the whole advance would have ground to a halt. The attacking elements would have to had to turn around to seal the locations. This would force more and more of their combat elements to guard the flanks so that after a few hundred miles there would be nothing left to attack with.
The fact that this did not happen was a result of the Iraqi central command structure where nothing could be done without orders which had been indoctrinated into them for decades.
This lack of "extra" units by the USA is a direct result of cutting out more and more personnel and compensating for the cuts by increasing firepower per person by substituting air power.
The US military has shown that it can win individual battles against enemy formations and small units by overwhelming firepower when air power or tanks are around. This does not negate the need to control the land behind the battle line, or all the land when there is no "front line" on a map. Iraq is not like France during WWII. The terrain is so different that to hide in the woods and move along unseen roads is not as easy as it was for the Resistance forces in France. The lack of people on the ground to be seen and to guard the ground - not once a day every day as they walk through at 10 AM - but troops all along high use roads, at every bridge, working with the local police (like what occurred in Germany after the 2nd WW) so people see the troops as they go around their normal everyday work (in which the military units act more like police than military troops) with their everywhere presence makes it difficult to impossible to coordinate, plant bombs, or move anonymously around.
This lack of regular line combat divisions in support garrison roles is a direct result of the Republican and Democratic policies since the late 1970s of replacing people with technology in order to compensate for loss of field divisions.