Caste System, also called Casteism is a system of governance in which groups of people are separated into socio-economic groups by job classification (and later birth) and are generally only allowed to marry within their caste, often by family rules. Caste systems, as opposed to other forms of governance were especially common in South Asia, albeit similar ideas were prevalent around the world, such as the Edo System of Japan.
In a Caste System there are traditionally four castes/varnas: 
The religious caste, 
The military caste, 
The commerce/landowner caste, and 
The menial labour caste. Albeit, land owning farmers were considered as a member of the commerce class. With there sometimes being 'untouchables' who are outside the caste system and specifically condemned due to their sins or untechnical life.
Doctrine & History
The original manifestation of the Caste System was in Hinduism, from the Varnas. Varnas were classifications of different jobs, and their duties in society. The goal of the Varnas was to classify people on their job and skill, and dedicate duties to each varna. Originally, the caste system was not inheritable, and it was decided on your education, skill, personality, and career. A member of the commerce class could join the ruling class if he took over, and was assertive enough to rule. The same could go for a ruling class member, who could go down to become a laborer if he was not effective and was lazy, and lost his power. Of course, children often were like their parents, and received a similar education, allowing children to be the same Varna as their parent. An example of a change in roles is how the founder of the Gupta Empire was a member of the commerce class, but took over the Empire. There was untouchables back in the day, and they were considered people who were the worst of sinners, barbarians, and unethical men.
Once the British conquered India, the idea of a birth-right caste system was born, as Brahmins (Religious Caste), were told of their superiority over everyone else, and the idea was propagated. While not the original manifestation, it soon became the more popular theory, and made the Caste System from a flexible social order into a rigid one. In the modern days, it has slowly returned to a flexible one, but there is still much influence from the birth-right theory.
Relationships
Upper Caste Brahmins
Hindu Theocracy - I'm honored that you chose me as your social system!
Monarchism - The favorite of the Caste System. Every society needs a ruler at the top!
Absolute Monarchism - I think that the most able should rule, so you kind of scare me. Nevertheless, you do have the god-given right to rule, and most of the time, you are an enlightened fellow.
Feudalism - My based European counterpart.
Combatocracy & 
Stratocracy - Kshatriya!
Esoteric Fascism - My supporter from Germany, though he acts rather weird at times.
Reactionaryism - And my supporter from Italy
Reactionary Socialism - Best leftist!
Lower Caste Shudras
Hindutva - You used me when necessary and marginalized me when I was a liability. Savarkar also attempted to destroy me, you deranged bigot!
Social Democracy - Hinduism says to donate to the poor, but you throw away the idea of a social hierarchy. What do you have against rulers and followers?
Elective Monarchism - When I meant "the most able should lead", I didn't mean that. But hey. Monarchism is Monarchism.
Untouchable Pariahs
Marxism–Leninism–Maoism - Evil.
Enlightenment Thought - I don't hate you, we both love science and arts! But why are you so against social hierarchies? There needs to be a natural order.
Marxism - You Marxists are tearing apart social order.
Gallery
Portraits
Alternative designs
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Slavery
Further Information
Wikipedia
- Caste
Caste system in India
Caste system in Nepal
Caste system in Pakistan
Caste system in Sri Lanka
Balinese caste system
Caste systems in Africa
