Obviously the US military has seen plenty of combat since World War 2. Why was there no congressional declaration of war in Korea, Vietnam, Iraq, or in any of the other conflicts of the 20th century's latter half?
While the question is simple enough, the answer is (naturally) complicated. It depends on a number of factors including how declarations of war technically work, the specific nature of the post-WW2 conflicts, and sadly, political climate. I'll try to elaborate on each of these factors:
War Declarations: Congress has only formally declared war 11 times across 5 conflicts (War of 1812; war against Mexico in 1846; war with Spain in 1898; WW1 and WW2). By declaring war, both the legislative and executive branches gain sudden and enormous emergency powers in order to mobilize the country for war and deal with foreign threats. We're talking MAJOR changes to the way people live their daily lives, up to and including possible suspension of Constitutional rights. As such, Congress logically looks to avoid opening up that door unless it's deemed truly necessary.
Post-WW2 Conflicts: Along those same lines, our forays into Korea/Vietnam/Iraq did not merit a formal declaration of war against those nations. The Korea and Vietnam conflicts were civil wars where the U.S. felt it had a stake in the outcome, but it's not like these were united nations taking up arms against the U.S. such as with Great Britain in 1812 or Germany in 1917. Similar situation in Iraq where we had a stake in Gulf Regional stability but that's about it. Furthermore, the passage of the War Powers Resolution in 1973 made it easier for the President to deploy troops under certain conditions without Congressional approval or a formal declaration of war.
Politics: simply put, no one in Congress is likely to stick their neck out to formally declare war if it could cost them their jobs. Even the War Resolution against Iraq has become highly politicized; imagine how much worse it would be if the U.S. had formally declared war in that conflict, which could have opened the door for a reinstated military draft or mobilizing the country into a wartime economy. (I'll leave it at that because it's hard to elaborate without stepping on partisan political landlines).
TL;DR: because formally declaring war involves drastically changing the way the U.S. operates, these conflicts were not deemed necessary for formal DoWs, troops could be deployed without such a declaration anyway, and no one in Congress wants to deal with the negative consequences of formally declaring war if it goes poorly.
Sources:
Ahh, actually been reading a lot about this as it is integral to larger conceptions of the intersection of foreign policy and American law.
First, put aside the Korean War, as the legal framework for that war was far different from most U.S. conflicts. There is a convincing argument that the framework was actually illegal, or at least it would be if applied today.
Art I ยง8 cl. 4 of the U.S. Constitution reads: "To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water." This is generally called the War Powers Clause.
However, the declaration of war has a particularly formal meaning, it implies a state of perfect war (this has implications when it comes to international custom and law.) Force can still be exercised in states of imperfect war, and Congress can effectively dole out limited authorizations of force (a good example of this would be the Quasi-War with France)
So you really have two separate concepts, the declaration of war and the authorization of force. This can be seen in formal declarations of war:
"Let it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That war be and is hereby declared to exist between the United Kingdom of Great Britain and Ireland and the dependencies thereof, and the United States of America and their territories; and that the President of the United States is hereby authorized to use the whole land and naval force of the United States to carry the same into effect, and to issue to private armed vessels of the United States commissions or letters of marque and general reprisal, in such form as he shall think proper, and under the seal of the United States, against the vessels, goods, and effects of the government of the said United Kingdom of Great Britain and Ireland, and the subjects thereof."
This is the declaration of war for the War of 1812. Notice the italicized text (italics added by me), this statute both declares war and authorizes force. What has happened post-WWII, for a variety of reasons, is that the formal declaration of war just doesn't occur anymore (this isn't a strictly U.S. thing, its a global phenomena) part of this is that the formal international laws and customs of war have been codified by treaty and now apply to most authorized uses of state force, so that the difference between authorized force and declared war is minimal.
Now, authorization of force is still necessary to engage in armed conflict. The president can deploy forces in emergency situations or in self-defense of the nations, but under the War Powers Resolution, the president must get congressional authorization for the use of force or withdraw the forces within 60 days (there is an emergency 30 day extension provision, but it can only be used once.)
Just as an example, this is the authorization for the use of force in Iraq (just copying the specific section, whole thing is publicly available):
"Sec. 3. Authorization for Use of American Armed Forces.
(a) Authorization. The President is authorized to use the Armed Forces of the United States as he determines to be necessary and appropriate in order to
(1) defend the national security of the United States against the continuing threat posed by Iraq; and
(2) enforce all relevant United Nations Security Council resolutions regarding Iraq."
Note how similar it looks to the authorization provision in the earlier declaration of war.
There is still some support for the idea that a conflict as large as another World War would require a proper declaration of war, but that is untested.
I have three follow up questions, if someone would be so kind.
I've also heard that one of the advantages of not officially declaring war through the Senate is that the budget for such military activities can stay somewhat obtuse. Anyone have any clarification?
My suspicion is that the lack of declaration has more to do with the power of the aftermath of such a vote politically. We can see examples of what that can do when it comes to the second war in Iraq. Were Senators (in any of these wars) wary of being brought an up of down vote because of perceived political cost or was it something else - was being brought an up or down war vote out of their hands?
This activity is part of the historical narrative I've heard of an expanding executive branch over the last 60-70 years. Is this is accurate and, if so, is it the symptom of political convenience or from a direct effort from the executive branch to expand power?