Congressional and Presidential War Powers under the US Constitution
You may hear on the news that the United States is at war with Syria, Iraq or ISIS. Technically, though, the United States is not “at war” with any of those under the constitutional definition of the term because Congress hasn’t declared war. Congress has not, in fact, declared war since 1942 (when it declared war on Hungary, Romania and Bulgaria during World War II). Does that mean that there was no Korean war, no Vietnam war, no war during Operation Desert Storm in 1991 or during a host of other engagements that the US has been involved in since World War II? Well, not quite. While Congress has the sole power to declare war, the President disposes of the United States military.
The Constitutional Framework
The framers of the Constitution divided war powers between the power to declare war and power to direct war. Article I, Section 8 of the Constitution reads, “Congress shall have the power…to declare war”  and Article II, Section 2 names the President as commander-in-chief of the armed forces. 
This dichotomy is an example of checks and balances in action. The framers realized how important a decision it is for the United States to go to war and wanted to prevent any single entity from making it. Abraham Lincoln opined while in Congress: “…no one man should hold the power of bringing (that) oppression upon us.”
How War is Declared-Japan and World War II
Congress has only declared war eleven times in the history of the United States, but taking a closer look at one of these declarations will illustrate how the process works. On December 7, 1941, the Japanese military attacked Pearl Harbor, a U.S. naval base in Hawaii, and destroyed much of the United States’ Pacific fleet. The next morning, President Franklin D. Roosevelt approached Congress and formally requested that the United States go to war.
President Roosevelt told members of Congress that the unprovoked attack by Japan served as justification for committing the United States to join World War II. Furthermore, he asked that Congress authorize his use and control of the United States’ military forces.
In this situation, Congress immediately pulled all pending legislation related to Japan, considered President Roosevelt’s declaration as a joint resolution, and suspended some procedural rules that would slow down the approval process. It took less than a day for Congress to declare war. The joint resolution passed the House of Representatives and Senate nearly unanimously.
What Happens Afterwards
Once a declaration of war has been approved by Congress, a “state of war” under international law becomes effective. This means that the United States may commence “the killing of enemy combatants, the seizure of enemy property, and the apprehension of enemy aliens.” Additionally, the declaration of war terminates all diplomatic and commercial relations between the United States and its adversary and suspends most treaties that the two have signed.
An official declaration of war has ramifications in the domestic sphere as well. When Congress declares war, many “standby statues” are automatically activated, conferring special powers onto the President. These powers can have drastic consequences. For example, under one statute, the President can order manufacturing plants to produce armaments for the military. If the manufacturing plants refuse to do so, the President can order the military to seize the plants. Another statute allows the President and executive agencies to conduct electronic surveillance without a court order for some time after Congress declares war.
A formal declaration of war also activates the Alien Enemy Act, allowing the President to apprehend, restrain, secure, and remove all natives from, or citizens of, the hostile nation from the United States, unless these people have been naturalized. For example, during World War I, President Woodrow Wilson used the powers conferred by this Act to prevent German aliens from possessing firearms or explosives.
In addition to Congress’ ability to declare a war, it also has the power to oversee it and most importantly, determine how and whether it is funded.
First, Congress, not the executive branch, has “the power of the purse” over the military. Article I, Section 8 says that Congress has the power “To raise and support Armies.” If Congress decides that it does not want to allocate a budget to military matters, such as the manufacture of additional weapons or the raising of more soldiers, it can decline to do so. Thus, Congress can place financial hurdles in front of the President and make a war extremely difficult for him to wage.
Congress can also affect the United States’ status in a war by declaring war on some enemies while declining to do so in the case of others. For example, in World War II, the United States declared war on Germany, Italy, Japan, Bulgaria, Hungary and Romania, but not on Axis participant Finland.
Congress can define the nature of war by limiting the scope of a declaration of war, though this has never actually been done. Finally, Congress can declare an end to a war by passing legislation that cancels the existing state of war. Like any other piece of legislation, however, this can be vetoed by the president (though as always, the veto can be overridden by a two-thirds majority of Congress).
Unilateral Presidential Actions
So, if the United States has not declared war since 1942, how is it that we been involved in so many military actions since? The answer is that as commander-in-chief of the military, the president can simply order the military about without a declaration of war, and virtually every president has taken advantage of this ability.
Though Congress has stopped short of declaring war, Congress has given the president express authority to conduct military actions several times since World War II, including the Gulf of Tonkin Resolution in 1964 that led to the Vietnam “War” and Authorization for Use of Military Force in 2001 while led to military actions in Afghanistan.
After the Vietnam War, Congress did pass the War Powers Resolution of 1973, which limited the President’s power to engage in foreign military actions without congressional consent. However, the enforceability of this resolution is unclear. As a practical matter, no Presidential military action has been successfully challenged under the War Powers Resolution.
While the declaration of war may be a thing of the past in United States diplomacy, Congress retains means to affect the President’s ability to conduct military actions. As such, the constitutional split of military powers between the president and Congress remains very much in effect.
 USCS Const. Art. I, § 8,
 USCS Const. Art. II, § 2
 10 USC § 2538
 50 USC § 1811
 USCS Const. Art. I
 Christopher Yoo, “The Unitary Executive in the Modern Era,” 1945-2004, 90 Iowa L. Rev. 601, (2005).
 See, e.g., Campbell v. Clinton, 203 F.3d 19 (D.C. Cir. 2000)