Why do you think the Army National Guard got all Combat Arms and the Army Reserve got the support missions ?

The realignment of CA to the Guard, and CS/CSS to Reserve took place in the early 90s under Clinton. When he reduced the AD manning, most of the CS/CSS units were cut. To maintain AD fighting strength, those units went to the Reserves (which keeps them under the federal umbrella). The Guard picked up the strategic reserve CA job. One of the reasons the Guard is CA focussed is that we are the primary line of defense for the homeland.

The Guard got the Combat Arms jobs because that is what they wanted and asked for, and what their governors asked for as well, so I guess they need to be careful of what they asked for? The National Guard is tasked with managing civilian unrest at the State level.

It's a combination of factors.

First there is the Constitutional factors such as the Army Clause, which creates and expanding and contracting Army, but does not affect the "Militia" (the Guard, which has become the de facto Militia).

The you have the Posse Comitatus Act, which prevents the Army from being used in an LE fashion, but which does not have the same restrictions on the Guard/Militias (State level forces).

Third is that you have three (3) separate entities vying for what is essentially one "pot" of money. If you had two "reserve" forces with similar missions, which shared resources, they would destroy each other. Stepping back from the Army (et al) for just a second, and look at the Services. Each is VERY distinct in their missions, though there is some overlap. The Army and the Marines don't really "fight" for resources. The Navy and the Air Force don't really "fight" for resources.... but if things were arranges just a hair differently.... we sure as hell would.

So as a pragmatic approach, CA goes to State Level. CS/CSS goes to Federal Reserve. Federal Active gets everything and can tap either as needed.

Some great responses. The latest change did take place in the early 1990s. Going back to the end of Vietnam after so many Soldiers were individually drafted and rotated thru the Army Chief of Staff GEN Creighton Abrams rewrote some of the policies to help ensure we never went to war again without the Reserves and National Guard. When the National Guard and Reserve decided to give most of the Combat Arms to the National Guard and most of the CSS assets to the Reserves it made more sense since the reserves are a federal force where individual members can be plucked out and mobilized. The Guard is supposed to be mobilized as units. Because Combat Arms requires a lot more collective training from the fire team up it makes more sense keeping the Infantry, Armor, Aviation and Artillery even Special Forces under the states. A truck driver, or rigger or cook doesn't need to be able to act as a team as immediately as a trained gun section needs to react. Another advantage is the fact that National Guardsmen train together for years sometimes decades where as Active folks are lucky if their unit remains intact for even a year or a deployment. Don't forget however the Reserves still has it's share of combat arms to include the 442nd Regimental Combat Team in the US Territories in the pacific mostly American Samoa and Guam. The Army Reserve maintains units such as Mortuary Affairs and Water Purification due in prt to the fact during peace time the Active Army or National Guard isn't going to have much call for those units 365 days a year. The difference between Title 10 and Title 32 plays another important fact as well! Finally I believe the Chief of the Army Reserve at the time felt it would be a lot more beneficial for the Reserves to maintain the bulk of the CS and CSS assets of the Army.

Well, if you see what happen back in middle 90's I was in the reserves than and they deactivated the infantry unit I was in.

Although AD has some support abilities the majority falls within the Reserves, same goes for NG. The reserves supports both depending on the need of the mission. Reserves can assist the NG for DSCA (homeland) missions when asked by the NG. The "Militia" needs to maintain their ability to protect and defend the people of the U.S. that is much harder to do if your main mission is to support the fight first and get in the fight second.

Because it can be called up to respond, what a lot of active duty people fail to realize is that they can be called up to reinforce the national guard.

The transition of combat arms to the NG was a result of Vietnam and the total force policy - The NG wasn't fully used yet there was a draft during Vietnam. So thinking in cold war terms - the NG would act as reserve manpower to augment combat formations in mid to high intensity wars against the Warsaw Pact. To satisfy this requirement, Guard units had to be equipped and trained as armor, mechanized infantry, and artillery combined arms teams. The politicians loved this plan as it translated into dollars for their states. So this became the plan in the late 80's and early 90's. However during the 90's the active military cuts were to deep and thus the Guard was called upon heavily to support OEF and OIF. Until then the congressman, governors, and the state adjutant generals got exactly what they wanted financially and politically. That is, until OEF and OIF. The move was put into play in the late 70's and is all about money hungry politicians not about putting down civil unrest. However the NG is in a unique position of being under the state authority in peace times for state emergencies like hurricanes or civil unrest and under the authority of the President in times of federal emergency.

When the military was cutting back when Clinton was in office. The guard asked for the combat arms. They got what they asked for. The reserves got the support units

In the early formation of the U.S. The states had an obligation to maintain their militia, they hold primarily combat positions in the event of an unjust act by federal government. The state needs to maintain a capable militia in order to react without having to retrain support based soldiers limiting capacity to react quickly.

During wartime it is also being reinforced by giving govt funding to arm the state during war time by providing equipment and govt subsidies/funding. So naturally state senators will always be eager to send the NG in a combat fashion.