It is indeed a bad thing to live under a prince with whom nothing is lawful, but a much worse to live under one with whom all things are lawful. (Institutes 4.11.10)

As we continue Calvin's look at the civil magistrate it is increasingly clear that Calvin stands in the middle of a very wide gap. He strongly affirms the vocation of the magistrate before God. The magistrate owes God its obedience. But he also firmly establishes a freedom for the magistrate. The latter remains to be seen. The former is found in his affirmation of punishment and the death penalty,

"How can magistrates be at once pious and yet shedders of blood? But if we understand that the magistrate, in inflicting punishment, acts not of himself, but executes the very judgments of God, we shall be disencumbered of every doubt. The law of the Lord forbids to kill; but, that murder may not go unpunished, the Lawgiver himself puts the sword into the hands of his ministers, that they may employ it against all murderers. It belongs not to the pious to afflict and hurt; but to avenge the afflictions of the pious, at the command of God, is neither to afflict nor hurt." (Inst 4.11.10)

The power of the sword is bestowed solely on the magistrate. It does not belong to pious individuals. But the power exists because God has given it. Therefore, it must be yielded to God and God's authority. It is this responsibility before God that brings Calvin to say,

"The magistrate must guard against both extremes; he must neither, by excessive severity, rather wound than cure, nor by a superstitious affectation of clemency, fall into the most cruel inhumanity, by giving way to soft and dissolute indulgence to the destruction of many." (Inst 4.11.10)

Calvin follows up this discussion of the sword with a section on war. If it is properly the magistrate's right to wield the sword in punishment then the sword also belong to the state in defense and war. 

"If they justly punish those robbers whose injuries have been afflicted only on a few, will they allow the whole country to be robbed and devastated with impunity? Since it makes no difference whether it is by a king or by the lowest of the people that a hostile and devastating inroad is made into a district over which they have no authority, all alike are to be regarded and punished as robbers. Natural equity and duty, therefore, demand that princes be armed not only to repress private crimes by judicial inflictions, but to defend the subjects committed to their guardianship whenever they are hostilely assailed. Such even the Holy Spirit, in many passages of Scripture, declares to be lawful." (Inst 4.11.11)

Calvin is no pacifist. The laws of the land protect people. So also, the sword must protect the nation as a whole. The definition of a just war is defence. This does not entirely mean waiting for the other to strike first. But a clear "defend the subjects committed to their guardianship." Even as libertarian might recoil in frustration at elements of Calvin's thought, his brief discussion on war is right on the target. America has grown fond of decreeing that every threat in the world is a threat upon America. In this way, the government disguises its unfortunate bloodlust. Yet, Calvin is clear. The defence is to be supplied only when "they are hostilely assailed." Get our troops off of foreign soil and return to a true Christian magistrate.