All of these things are purposes that the military is used for, but there is another way to look at the question. Quite simply, the Department of Defense is a bureaucracy. Whatever the purposes that people think that it exists for, as a bureaucracy its primary purpose is survival and growth. Any organism grows and thrives or it declines and dies. A bureaucracy is no different.
The political climate for the past eight years has demanded that the military shrink to a shadow of its former self. Needless to say, the organism doesn't like that. It will attempt to survive, and to grow again.
Now, this doesn't mean that the military is going to run amok. Our military has a long history of avoiding politics (until after retirement, anyway) and following orders. Simply stepping up and taking what they want is not an option in the institutional mind set of our military forces.
If the military can't just take what it needs, what does it do? The solution lies in the fact that the military is not a monolithic structure. Most people realize that there are four military services, and think of each one as a unified structure. Most people are wrong already. There are five military services and two more "uniformed" services that are not actually military. The "Big Four" are, in order of seniority, the Army, Navy, Marines and Air Force. The fifth military service is the Coast Guard (between the Army and Navy in seniority); and the two non-military uniformed services are the Public Health Service (that's why you see the Surgeon General wearing an Admiral's uniform), and the National Oceanographic and Atmospheric Administration; but these three are normally under departments other than DOD, and have only a peripheral effect on its budget.
Far from being monolithic, the services are each composed of a plethora of sub-groups that pull in every imaginable direction. As an example, let's look at the Navy.
The Navy has ships and aircraft, and the people who operate them. It should be a fairly simple organization, but it's not. The different communities (read, special interest groups) are mind-boggling in their numbers. Each type of platform has its own needs and forms its own groups and sub-groups. The brown shoes (aviation) and the black shoes (everybody else) each advance their own agendas at the expense of the other. Within each of these major groups, sub-groups form.
