In regards to "national interest" could you cite that in the Constitution?
The following is all the constitution has to say on this matter. Congress has the authority to declare war. It is not limited to survival or when attacked. That is the decision of congress and it can included "national interest".
Now when it talks of congress calling the militia to suppress insurrections and repeal invasion that is talking about the state militia commonly known as the National Guard. These troops are different than the US Army and fall under the control of the sate governor until called forth by congress. There is nothing in the constitution that limits the reasons for congress to declare war.
To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;
To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;
To provide and maintain a Navy;
To make Rules for the Government and Regulation of the land and naval Forces;
To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;