The four theories of state origin are evolutionary theory, force theory, divine right and social contract. The vast majority of the states in the world today originate from social contract. This is essentially a constitution in which the members of the state give a mandate to the elected few to rule the country.
In such states, it is important for both the leaders and the rest of the population to follow the stipulations in the constitution, which is drawn up by both parties.
The evolutionary theory of origin states that most states evolved from family. The force theory is also applicable in many states today. It relies on the use of aggression to come to power. This is one of the most common forms of state origin in countries that were colonized and which subsequently became independent after armed struggle.
The theory of divine right states that the leaders of a state come about as a result of ordination from God. This is not such a common method of state origin these days, though it was one of the most popular in the past. The Crusades and conquests of various parts of the world by Islamic leaders are prime examples of this.