Max Weber provided the simplest definition: “A government is an institution that holds a monopoly on the legitimate use of violence.” Another, fancier way he phrased it is “A state is a human community that (successfully) claims the monopoly of the legitimate use of physical force within a given territory.”
So far as social theories go, I’m a Conflict theorist, and I like Max Weber’s teachings more than Karl Marx. Lord Acton wrote “The History of Freedom in Antiquity”.
Here’s an excerpt:
“Two men’s lives span the interval from the first admission of popular influence, under Solon, to the downfall of the State. Their history furnishes the classic example of the peril of democracy under conditions singularly favorable. For the Athenians were not only brave and capable and patriotic and capable of generous sacrifice, but they were the most religious of the Greeks. They venerated the Constitution which had given them prosperity, and equality, and freedom, and never questioned the fundamental laws which regulated the enormous power of the assembly. They tolerated considerable variety of opinion, and great license of speech, and their humanity towards their slaves roused the indignation even of the most intelligent partisan of aristocracy. Thus they became the only people of antiquity that grew great by democratic institutions. But the possession of unlimited power, which corrodes the conscience, hardens the heart, and confounds the understanding of monarchs, exercised its demoralizing influence on the illustrious democracy of Athens. It is bad to be oppressed by a minority, but it is worse to be oppressed by a majority. For there is a reserve of latent power in the masses which, if called into play, the minority can seldom resist. But from the absolute will of an entire people there is no appeal, no refuge but treason. The humblest and most numerous class of the Athenians united the legislative, the judicial, and, in part, the executive. The philosophy that was then in the ascendent taught them that there is no law superior to that of the State – the lawgiver is above the law.
It followed that the sovereign people had a right to do whatever was within its power, and was bound by no rule of right or wrong but its own judgment of expediency. On a memorable occasion the assembled Athenians declared it monstrous that they should be prevented from doing whatever they chose. No force that existed could restrain them, and they resolved that no duty should restrain them, and they would be bound by no laws that were not of their own making. In this way, the emancipated people of Athens became a tyrant, and their government, the pioneer of European freedom, stands condemned with a terrible unanimity by all the wisest of the ancients.
They ruined their city by attempting to conduct war by debate in the marketplace. Like the French Republic, they put their unsuccessful commanders to death. They treated their dependencies with such injustice that they lost their maritime empire. They plundered the rich until the rich conspired with the public enemy, and they crowned their guilt by the martyrdom of Socrates. The repentance of the Athenians came too late to save the Republic. But the lesson of their experience endures for all time, for it teaches that government by the whole people, being the instrument of the most numerous and most powerful class, is an evil of the same nature as unmixed monarchy, and requires, for nearly the same reasons, institutions that shall protect it against itself, and shall uphold the permanent reign of law against arbitrary revolutions of opinion.”
John Emerich Edward Dalberg, Lord Acton
Trego's Mountain Ear 