To quote, "Either you go to war or you do not."
With that is the implication that the United States can only "win wars" that it has fully dedicated itself to do.
The problem arises from both the political and physical implications of committing war. For instance, in reflection of a previous military intervention in the Mediterranean Sea, pirates operate off of the coast of Somalia. These pirates regularly threaten United States' shipping, thus economic survival. They have taken ships and hostages from allied nations. Should they be allowed to continue to do so and grow their operation without intervention, they could shut down the passage way through the Suez Canal. This would certainly harm the United States and its allies economically and even militarily if we were unable to safely transit ships, men and supplies through this passage way.
By their location and nature, there is no force that can interdict these operations except by ship. The only force that the United States has capable of interdicting these pirates is the United States Navy. Obviously, by their acts and our need to defend shipping, it is likely that a violent confrontation would occur (and did with the French rescuing hostages and killing pirates). Is this an act of war? Particularly, as these pirates are by international law, "out laws", who are not acting on the direction or purpose of the recognized, legitimate government of Somalia.
Do we "declare war" with an official "declaration of war" on "pirates" before sending or using military force? If not, why not? The first issue is that "pirates" by their nature and legal status of being "outlaws" are "illegitimate" parties. To declare war against them, by implication of bringing the entire power of the United States (ie, economic, political and military), it recognizes these forces as "legitimate" and worthy of that onerous attention. Further, under both the written and unwritten rules of warfare, certain niceties would have to be accepted. Such as recognizing flags of truce, negotiating with an appointed representative or otherwise recognizing some legitimate (ie, lawful) complaints that need to be resolved.
Of course, pirates, by their nature preying on the weak and unprotected, acting outside of the laws of their own nation and recognized international laws, robbing people of life and property, without any legitimate cause accept to enrich themselves, have no "legitimate" complaints.
Still, to interdict them and to safeguard "interests of the United States", it will require "military force". Does that require a declaration of war? Does it even require Congress to issue an Authorization to use Military Force? Under the current separation of powers, the President being the Commander in Chief of the military forces whose function is to defend the United States against "all enemies", but "pirates" being illegitimate parties outside the law without any legitimate claims to Congressional (thus, legislative) time, the answer seems to be "no". Certainly, there is no current act or law by Congress authorizing military operations against Somalian pirates. But, we do.
Should we instead declare war on Somalia? If so, what government do we declare war against? The current recognized government of Somalia who is ostensibly a nominal ally of the United States against Islamist forces, partially underwritten, trained and inclusive of Al Qaeda allied organizations or actual members? Maybe we should simply ask for permission of the "Somalian" government, to put forces in their nation and attack these other forces? They likely receive money from piratical activities anyway. Then again, we would end up like Iraq. Or, worse, considering past history and complete lack of real social constructs for more than two decades.
Let's look at a few more current military activities. Operation Enduring Freedom in Afghanistan. Did we "declare war" on Afghanistan? Why did congress simply authorize the use of military force instead of declaring war on Afghanistan?
The first issue is that Afghanistan was governed by the Taliban. The Taliban government of Afghanistan was not the legitimate recognized government of Afghanistan. At least, not by the United States. While we may have demanded that they turn over bin Laden, we had few hopes that they would nor did we consider them anything more than an organization as a means to a way. Certainly, we did not offer any legitimate (ie, legal) treaty with them for security, political recognition or economic trade. Congress did not even consider it. To do so would have recognized that government as the lawful government of Afghanistan.
By the same token, we would not legitimate such a government by "declaring war". At the same time, the Taliban were supported by and nominal allies of Pakistan. In many respects, even moving significant forces, the president legally could act to defend the United States. However, by acting militarily against the Taliban, had Pakistan not felt significantly secure and had mobilized its forces, it could have brought on a regional or even international crisis. Because, as soon as Pakistan mobilized, India would have mobilized and possibly Tajikistan, Uzbekistan and so on. Who would have caused Russia to become nervous and who might also have felt compelled to mobilize, if not interfere.
In such a case, the President would need to legally be covered by at least the minimal of an authorization to use military force from congress. In which case, Congress would be duly and legally informed of the acts and implications should something more drastic had occurred and required additional action. Additionally, had the United States officially declared war on Afghanistan, meaning its people, its political, military and economic resources, Pakistan may have felt legally and morally bound to act in its defense. Possibly even being forced by popular demand to declare war. With all of the regional and international implications previously noted.
In the end, it is one of the significant reasons why the United States parsed its political statements and eschewed a declaration of war. In effect, to separate our military action from "the people" of Afghanistan and establish exactly who and to what limits we would go in committing our military forces. In a real and legal sense, giving Pakistan no reason to intercede or act in any way. Of course, we sweetened that deal with a military, economic and political agreements.
To paraphrase Clausewitz, all politics is war and all war is politics
In regards to bin Laden and al Qaeda, the same reason why we did not "declare war" on the pirates of Somalia applies to these as well if not more so. Terrorists, by every convention, written or or unwritten, are "outlaws". They have no legitimate standing with any government. Even governments that support them do so in as much a way as possible to distance themselves from any real or "legal" connection, beyond possibly verbalizing support for their complaints. Sometimes, these connections are "known", but for political reasons, may go unchallenged in order avert other political implications. Like escalating war.
Like the pirates, bin Laden's location in another country, surrounded by somewhat significant paramilitary forces, in fortified positions with some support among the population that could act to intervene or add to his forces, would seem to necessitate military force. Particularly, as he and his organization were considered an imminent threat. Still, we would never legitimate his organization or his complaints with a formal "declaration of war". The need for an authorization to use military force arises from the geo-political realities as much as meeting any legal (ie, Constitutional) requirements.
There are many such implications and variations that effect the actions of the President and Congress in defending the United States. Not all of them require the full power of the nation at war.
Of all of the implications, the most important to remember is that, yes, when the United States Congress Declares War, it does obligate and bring to bear the entire political, economic and military power of the United States. That may include obligating or putting at risk any allied or friendly nations. In doing so, through the Congress, our legislative body, it legally recognizes the opposing force as a legitimate (legal) entity to both conduct war against as well as to negotiate an end to the conflict. Under such conditions, the United States, by internal law and signatory to such as the Geneva Conventions, would be legally bound to treat such an entity with all expected legal obligations including recognizing ambassadors or representatives, treating all military or militant forces as legal combatants, recognizing flags of truce, trading prisoners, negotiating peace and every other activity designated by such conventions, treaties and laws.
In the same respect, by bringing this force to bear, against an entire nation, it also calls into war the entire political, economic and military powers AND alliances of that nation as well as any nation that may believe that its interests are endangered by such a war.
It is the reason why the United States has, in fact, been circumspect in using this power to "declare war". To date, a total of five times. The last two times the United States "declared war" in the 20th century, it did win these wars. However, those wars were World Wars. The United States not only committed all of its power to those wars, but also placed them at risk. The last world war involved over 58 countries and cost 72 million lives directly or related to war.
A declaration of war may, in fact, be the deadliest and most destructive weapon in the United States arsenal.
What of our treaty obligations? We have ratified many such mutual defense treaties where we have agreed to come to the assistance of an ally or defend a certain zone or choke point. Does an approval by Congress of this obligation negate the need to a formal declaration of war once the shooting starts. What additional legal requirements are necessary if Japan is attacked, or Poland gets into more then just words with Belorussia. I can see taking our time if Russia tries to take back Ukraine but hey...what if Bolivia and Venezuela gang up on Columbia?
It would really depend on the language of the treaty. For instance, Colombia, being a friendly nation, to my knowledge does not have a compact or treaty with the United States for mutual defense in national crisis. We have trade agreements and certain quid pro quo agreements for the policing of drugs and gangs, but these do not, as far as I know, extend to any national defense agreements.
We may have agreements to supply weapons and ammunition, amongst other things, over all and in general. In which case, we would likely continue to supply those items under that contract. We would probably not declare war against any invaders (Monroe Doctrine) unless something else occurred. Such as, if we had observers or if we were supplying equipment, food, etc to Colombia and the ships, planes or people were harmed by Venezuela or Bolivia, then it might call into play our obligations to defend our citizens and property. then again, congress and/or the president could decide to reduce our presence or activities there to reduce the risk.
On the otherhand, if say our embassies or some citizens were in danger, the President could simply send forces under "imminent danger" to secure or rescue them. Depending on the "imminence" of that danger, the President could ask for an AUMF if he believed that he had time and that it might be necessary to use some significant force to accomplish that security.
In the case of Venezuela and Colombia, without a formal treaty for mutual defense, the United States would only declare war if some significant and irreversible act occurred that directly threatened Americans, their property or some significant interest. For instance, Venezuelan military goes to our embassy, takes everyone hostage and takes them back to Venezuela as "prisoners of war". We could opt to treat with them and avoid war while parking ships off the coast. that would probably take an AUMF. Or, if we felt it was politically appropriate, we could declare war. Such as, if they execute a prisoner or ten or twenty. Venezuela, being ruled by a legally recognized government, committing such an act, could probably be considered performing an act of war and become a legitimate target and recipient of such a declaration.
Then again, if Venezuela has a mutual defense compact with say Argentina, Paraguay, etc, etc, and we were concerned about their possible reaction or inclusion in an expanding war that would destabilize the region, we might actually just authorize a use of military force with a stated goal of "rescuing the hostages" and "capturing the 'criminals' responsible". Thus, separating the country and people of Venezuela from the acts, limiting our own acts and, possibly, keeping these other nations (or just some) out of a greater conflict.
It would all depend on what we wanted or needed to accomplish. War as the continuation of politics.
You know, though, an interesting thought occurred to me last night. If we had Teddy Roosevelt in office, I think Mr. Chavez would indeed needed to fear the US when he nationalized the oil companies and confiscated land. Teddy, while not declaring war, very likely would have "spoke softly" (right) and put an American fleet off the Venezuelan coast.