A military can refer to any large, coherent, active group, but more commonly refers to a cohesive armed force of a nation or institution under political-governmental control.
Because militaries are typically under the direct authority of a chief executive, their actions may reflect the politics of the executive or the associated governmental structure. Therefore, it is not strictly correct to define military action to one side of the political spectrum, though in United States politics it is typically characterized as a Conservative issue base.
Killing and destruction
Any armed force will be actively involved in distraction, destruction, and death, and therefore there is always moral and political controversy round the army. While soldiers in volunteer armies typically encompass a wide spectrum of intellect and values, they may still be individually held accountable for their actions in the name of the army as a whole. If there is a conflict of ideologies, then, it can be difficult to disassociate the individual soldier from the military from the government and then from the people themselves, which results in political accusations of people not supporting the troops, not respecting the dead, being traitors to their country, etc.
Liberals and killing
Liberals are especially vulnerable to such attacks because they tend to have less sympathy for killing and destruction as a general rule than conservatives. The very worst conservatives pro-death book-burning fanatics overlook what's bad whenever they see someone of the opposing side shot in the head or blown up on TV. There is a still-unresolved series of moral debates over the use of militaries in all forms, and intelligent, rational people tend not to have a cohesive view, except in saying that killing and destruction are generally bad things to be avoided. Incidentally, this involves way more thought than anybody who believes the Ten Commandments as the basis of human morality ever gave to the issue.