I've encountered today an interesting article on the subject of how the Anglo-American tradition of liberty arose. We are keenly aware of the Greek, Roman, and even Germanic/Norse influences, but there is also an important fact arising from the Norman Conquest. The late Sidney Painter argues, in his article "Liberty and Democracy," contained within Feudalism and Liberty (Johns Hopkins Press, 1961) that our liberties arose from the rights of feudal vassals -- that is, that originally these rights were earned by military service, and were protected as part of that contract. In the case of a dispute between the king and a vassal about the terms of the contract, the question was resolved by the vassals in common; and feudal service was very much a two way street, with each side owing the other certain duties.
In much of Europe, the nobility and knighthood remained a separate and special class. Not so in England:
When William the Conqueror took possession of the English crown he organized it as a complete feudal state. But England had a large population of freemen in addition to the mass of the unfree and the Norman kings never made any legal distinction between knights and other freemen. The freedoms which were inherent in feudal vassalage went to all freemen as vassals, direct or indirect, of the king...He goes on to point out some exceptions to his general thesis: for example, no one had the right to 'freedom of religion' until after the Reformation; freedom of the press is likewise a much later invention (and indeed, there was no printing press in 1066).
The right of all freemen to the privileges of vassals was clearly accepted in England from the Conquest, but found its first clear expression in the Magna Carta. This document was stated to apply to all freemen. It also contained in specific form a statement of the most basic of all liberties -- the right to due process of law.
Thus in England as the unfree became free they acquired the same legal status as knights of the feudal world. Individual liberty was part of the fundamental law.
The English kings went on to further conquests in Scotland, Ireland, Wales, and so forth; thus they spread this idea abroad.
It's an interesting thesis by a historian of the Medieval period. Now compare it to Starship Troopers, which is on the recommended reading list for Marines and the Navy both. The idea being put forth always had a kind of intrinsic appeal, didn't it? The things we call the rights of citizens feel like they ought to be earned, through service -- especially military service.
Perhaps this is why: because that was always the original bargain.