Not Another Undeclared War: UK Parliament Votes, Why Not US Congress? [View all]
http://www.thenation.com/blog/175970/not-another-undeclared-war-if-uk-parliament-can-vote-why-not-us-congress#axzz2dUSuWLkU

President Barack Obama talks on the phone with Nicole Hockley and families of the victims of the Sandy Hook Elementary School shootings in Newtown, Connecticut, in the Oval Office, April 11, 2013. (Official White House Photo by Pete Souza)
In the aftermath of the Japanese attacks on Pearl Harbor, President Franklin Delano Roosevelts immediate response was to appear before a joint session of Congress to ask for a declaration of war. Despite the fact that an attack on US soil had killed and wounded thousands of Americans, despite the clear threat of additional attacks, Roosevelt honored the separation of powers as defined by the Constitution, along with the clear requirement that the Congress shall have power
to declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water.
No president since Roosevelt has respected the Constitution sufficiently to seek a formal declaration of war.
They have had plenty of excuses: a United Nations Security Council resolution, a Gulf of Tonkin Resolution, a consultation with congressional leaders. They have interpreted the War Powers Act broadly. They have simply done as they chose.
But they have not obtained the formal declarations of war required by the Constitution.