For the last 60 years, a troubling thing has happened to our government. The expansion of executive power is truly frightening. Perhaps no where is it more frightening than in the realm of war. Since World War 2, we have for some reason assumed that the president can lead us to war because he is "the commander and cheif." However, that is innacurate.
Much of our system of government is based upon the Roman system. The writers of the constitution were well schooled in the classics, and they greatly admired the Romans. Under the Roman system, the executive branch was made of three members. It was called the triumverate. In order for a new policy to be implemented, all three members of the triumverate had to come to an unanimous agreement. However, the Romans were keenly aware that sometimes it could be difficult to get three people to agree. They realised that in times of war or national emergency, quick action might be needed, and that with agreement necessary, this might not be possible. Therefore, they decided that in times of national emergency, one of the members of the triumverate could rule alone for a period of six months. This is what the commander and cheif doctrine is based on.
The Constitution gives Congress the power to declare war. This power exclusively belongs to Congress. It gives the President the role of commander and chief. What this means is that in order to engage in war, careful deliberation is required. No one should be able to do it unilaterally. Therefore, in order to initiate a conflict, Congress should have to authorize it as a way of preventing needless wars. However, after the war has commenced, it is extremely unreasonable to run a war based on the agreement of over 500 people. Therefore, the power for the actual execution of the war must be ceded to one man, the President.
For some reason this now means that the president can start, and run a war. That is why we are in the mess we are in.