There are other quotations in the Miller decision, such as:
The General Assembly of Virginia, October, 1785, (12 Hening's Statutes) declared,
"The defense and safety of the commonwealth depend upon having its citizens properly armed and taught the knowledge of military duty."
It further provided for organization and control of the Militia, and directed that "All free male persons between the ages of eighteen and fifty years," with certain exceptions, "shall be inrolled or formed into companies."
and...
By an Act passed April 4, 1786, the New York Legislature directed: That every able-bodied Male Person, being [p181] a Citizen of this State, or of any of the United States, and residing in this State, (except such Persons as are hereinafter excepted) and who are of the Age of Sixteen, and under the Age of Forty-five Years, shall, by the Captain or commanding Officer of the Beat in which such Citizens shall reside, within four Months after the passing of this Act, be enrolled in the Company of such Beat.
and...
The General Court of Massachusetts, January Session 1784, provided for the organization and government of the Militia. It directed that the Train Band should "contain all able bodied men, from sixteen to forty years of age, and the Alarm List, all other men under sixty years of age, . . ."
and...
In all the colonies, as in England, the militia system was based on the principle of the assize of arms. This implied the general obligation of all adult male inhabitants to possess arms, and, with certain exceptions, to [p180] cooperate in the work of defence.
You might also take note of the definition of comprise, as well as the usage note, found
here:
1. To consist of; be composed of: “The French got... French Equatorial Africa, comprising several territories” (Alex Shoumatoff).
2. To include; contain: “The word ‘politics’... comprises, in itself, a difficult study of no inconsiderable magnitude” (Charles Dickens). See Synonyms at include.
3. Usage Problem. To compose; constitute: “Put together the slaughterhouses, the steel mills, the freight yards... that comprised the city” (Saul Bellow).
Usage Note: The traditional rule states that the whole comprises the parts and the parts compose the whole. In strict usage: The Union comprises 50 states. Fifty states compose (or constitute or make up) the Union....
Getting back to the quotation to which you objected,
"the Militia comprised all males physically capable of acting in concert for the common defense." It seems to me, in light of the other quotations listed here, the definition of comprise, and the usage note, that the sentence says the militia consists of, or is composed of, all males physically capable of acting in concert for the common defense.