The Constitution grants the power to Congress to declare war in which the last time that such a declaration of war was granted by Congress was in 1942, in which, the Senate unanimously approved a declaration of war against Rumania. Since, that time, no war declaration has been issued from Congress, yet America has been involved in wars that have cost the lives of thousands upon thousands of soldiers as well as civilians, in Korea, in Vietnam, in Afghanistan, in Iraq, and so on, ad infinitum.
It would be a mistake, though, to believe that it only has been since 1942, that the imperial Presidency has ignored Congress in its wartime activities, incursions, invasions, and engagements, for almost since the inception of the United States, this nation has been involved in undeclared wars against countries such as France, in 1798-1802, Colombia/Panama in 1903, and the Philippines in 1899-1913.
All of this basically signifies that America is an imperial power, so then, logically it so follows that it is not truly a representative government, because it does not consult upon some of its most vital decisions with those that represent the people, but rather that this imperial power behaves in the same sort of manner as governments that are essentially autocratic in format, and/or are enthralled to the military-industrial-technology complex of those respective countries.
Whether or not, America should have undeclared wars in the sense of responding to an international urgency, crisis, or justification, is debatable on a case by case basis, but what really isn't debatable is the apparent power that the Presidency has to simply declare war upon whomever that Presidency wants to declare war against, without consulting with the constituency of this country, so that, in fit, form, and function this is neither a democracy or a republic, and it most certainly is not a country of the people, for the people, and by the people, but rather the people do not have an effective voice on matters that are of the utmost concern.
When any government in its actual functioning, circumvents its own Constitution, through Executive Orders, and twists and turns clear definitions of what war is or is not, so as to make it appear that the President has the right to engage in what is for all practical purposes actually war with other countries, incursions of all sorts, and the search and destruction for terrorists all over the globe, then such a government as that, is a government unto itself, and further those representatives that make up the legislative branch of that government have a voice that is effectively silenced or is irrelevant for all those that do not support these undeclared war efforts.
What is good for the military-industrial-technology complex is often not going to be good for this country, for wars are the type of thing, that have real consequences, of which, many of those consequences are not for the betterment of mankind, but rather serve to be something akin to "blood for oil," or "blood for strategic locations," as well as "blood for profit."What makes America great is not killing foreign people or the collateral damage of all those civilians killed, injured, and turned into unwanted refuges throughout the world; but rather what makes America great is being that beacon of freedom and liberty, as well as providing a fair shot at the pursuit of happiness, especially for all those that are the wretched refuse of life, yearning for something transcendent and priceless in its value