Class conflict
Usage: When Marxists speak of class struggle, they define a class primarily in economic terms, i.e., by its relationship to the means of production. When anarchists like Bakunin speak of class struggle, they have a broader definition of "social class" which encompasses "notions of domination and privilege" in the political and cultural spheres as well as the economic. Bakunin believed the successful struggle of the dominated classes would achieve a revolution to depose the ruling elites and create a stateless or libertarian socialism, and that a prerequisite for successful revolution is class solidarity.
Marx's theory of history asserts that in the history of economic systems such as capitalism and feudalism, class struggle is "the central fact of social evolution." Indeed, the first sentence of Chapter 1 of the Communist Manifesto reads: "The history of all hitherto existing society is the history of class struggles." Marxists view the struggle's resolution in favor of the working class to be inevitable under plutocratic capitalism.

Oligarchs versus commoners in Ancient Greece: Where societies are socially divided based on status, wealth, or control of social production and distribution, class structures arise and are thus coeval with civilization itself. The rise of class structures eventually leads to class conflict. It is a pattern that has repeated since at least European classical antiquity as illustrated in the Conflict of the Orders and the slave revolt led by Spartacus.

Thucydides: In his History, Thucydides describes a civil war in the city of Corcyra between the pro-Athens party of the common people and their pro-Corinth oligarchic opposition. Near the climax of the struggle, "the oligarchs in full rout, fearing that the victorious commons might assault and carry the arsenal and put them to the sword, fired the houses round the market-place and the lodging-houses, in order to bar their advance."
The historian Tacitus would later recount a similar class conflict in the city of Seleucia, in which disharmony between the oligarchs and the commoners would typically lead to each side calling on outside help to defeat the other. Thucydides believed that "as long as poverty gives men the courage of necessity, [...] so long will the impulse never be wanting to drive men into danger."

Aristotle: In the Politics, Aristotle describes the basic dimensions of class conflict: "Again, because the rich are generally few in number, while the poor are many, they appear to be antagonistic, and as the one or the other prevails they form the government.". Aristotle also commented that "poverty is the parent of revolution", but did not consider poverty to be the only cause of revolution. In a society where property is distributed equally throughout the community, "the nobles will be dissatisfied, because they think themselves worthy of more than an equal share of honors; and this is often found to be a cause of sedition and revolution." Moreover, Aristotle said that it was wrong for the poor to seize the wealth of the rich and divide it among themselves, but he said that it is wrong for the rich to impoverish the multitude.
Moreover, Aristotle further discussed a middle way, between laxity and cruelty, in the treatment of slaves by their masters, averring that "if not kept in hand, [slaves] are insolent, and think that they are as good as their masters, and, if harshly treated, they hate and conspire against them."

Socrates: Socrates was the first Greek philosopher to describe class conflict. In the Republic, by Plato, Socrates said that "any city, however small, is in fact divided into two, one the city of the poor, the other [the city] of the rich; these [cities] are at war with one another." Socrates disapproved of oligarchies, in which members of a small class of wealthy property owners take positions of political power in order to dominate the large social class of impoverished commoners; and used the analogy of a maritime pilot, who, like the power-holder in a polis, ought to be chosen for political office for his skill, not for the amount of property he owns.

Plutarch: The historian Plutarch recounts how the Greek people participated in the class conflict between the aristocrats and the common folk. Financially oppressed by their indebtedness to the aristocrats, the mass of Athenians chose Solon to be the lawgiver to lead them to freedom from their creditors. The philosopher Georg Wilhelm Friedrich Hegel said that Solon's constitution of the Athenian popular assembly created a political sphere that balanced the competing socio-economic interests of the social classes of Athens:

The wealthy aristocratic party of the plain
The poor common party of the mountains
The moderate party of the coast
Participating in a war among the social classes of Ancient Greece was a dangerous political endeavour. In his book Parallel Lives, Plutarch wrote of two Spartan kings, Agis and Cleomenes, who  "being desirous to raise the people, and to restore the noble and just form of government, now long fallen into disuse, [they] incurred the hatred of the rich and powerful, who could not endure to be deprived of the selfish enjoyment to which they were accustomed."

Patricians versus plebeians in Ancient Rome: It was similarly difficult for the Romans to maintain peace between the upper class, the patricians, and the lower class, the plebs. French Enlightenment philosopher Montesquieu notes that this conflict intensified after the overthrow of the Roman monarchy.
In The Spirit of Laws he lists the four main grievances of the plebs, which were rectified in the years following the deposition of King Tarquin:

The patricians had much too easy access to positions of public service.
The constitution granted the consuls far too much power.
The plebs were constantly verbally slighted.
The plebs had too little power in their assemblies.

Camillus: The Senate had the ability to give a magistrate the power of dictatorship, meaning he could bypass public law in the pursuit of a prescribed mandate. Montesquieu explains that the purpose of this institution was to tilt the balance of power in favour of the patricians. However, in an attempt to resolve a conflict between the patricians and the plebs, the dictator Camillus used his power of dictatorship to coerce the Senate into giving the plebs the right to choose one of the two consuls.

Marius: Tacitus believed that the increase in Roman power spurred the patricians to expand their power over more and more cities. This process, he felt, exacerbated pre-existing class tensions with the plebs, and eventually culminated in a civil war between the patrician Sulla and the populist reformer Marius. Marius had taken the step of enlisting capite censi, the very lowest class of citizens, into the army, for the first time allowing non-land owners into the legions.

Tiberius Gracchus: Of all the notable figures discussed by Plutarch and Tacitus, agrarian reformer Tiberius Gracchus may have most challenged the upper classes and most championed the cause of the lower classes. In a speech to the common soldiery, he decried their lowly conditions:

"The savage beasts," said he, "in Italy, have their particular dens, they have their places of repose and refuge; but the men who bear arms, and expose their lives for the safety of their country, enjoy in the meantime nothing more in it but the air and light; and having no houses or settlements of their own, are constrained to wander from place to place with their wives and children."
Following this observation, he remarked that these men "fought indeed and were slain, but it was to maintain the luxury and the wealth of other men." Cicero believed that Tiberius Gracchus's reforming efforts saved Rome from tyranny, arguing:

Tiberius Gracchus (says Cicero) caused the free-men to be admitted into the tribes, not by the force of his eloquence, but by a word, by a gesture; which had he not effected, the republic, whose drooping head we are at present scarce able to uphold, would not even exist.
Tiberius Gracchus weakened the power of the Senate by changing the law so that judges were chosen from the ranks of the knights, instead of their social superiors in the senatorial class.

Julius Caesar: Contrary to Shakespeare's depiction of Julius Caesar in the tragedy Julius Caesar, historian Michael Parenti has argued that Caesar was a populist, not a tyrant. In 2003 The New Press published Parenti's The Assassination of Julius Caesar: A People's History of Ancient Rome. Publishers Weekly said "Parenti [...] narrates a provocative history of the late republic in Rome (100–33 BC) to demonstrate that Caesar's death was the culmination of growing class conflict, economic disparity and political corruption." Kirkus Reviews wrote: "Populist historian Parenti... views ancient Rome's most famous assassination not as a tyrannicide but as a sanguinary scene in the never-ending drama of class warfare."

Coriolanus: The patrician Coriolanus, whose life William Shakespeare would later depict in the tragic play Coriolanus, fought on the other side of the class war, for the patricians and against the plebs. When grain arrived to relieve a serious shortage in the city of Rome, the plebs made it known that they felt it ought to be divided amongst them as a gift, but Coriolanus stood up in the Senate against this idea on the grounds that it would empower the plebs at the expense of the patricians.