The alliance theory suggests that marriage between various groups creates horizontal ties, such as alliances and relationships of reciprocity and exchange, which are more significant in kinship systems than inheritance and the continuance of the vertical line of descent. This idea emphasized marriage-based interconnections between localized clans or lineages across tribal societies as more essential than a notion of common descent.
The Elementary Structures of Kinship, written by French anthropologist Claude Lévi-Strauss and first published in 1949, offered a fresh perspective on kinship systems and relationships and has served as the foundation for alliance theory.
In contrast to descent theory, Alliance theory focuses on the relationships created between groups via marriage rather than how they are formed.
Lévi-Strauss distinguished between “elementary” and “complex” structures. “Elementary” structures are those with a positive marriage rule, like having to marry someone from the category of cross-cousin. Complex structures are those with a negative marriage rule, as seen in Western societies where an individual can marry anyone who is not a close kin.
Elementary structures are further classified into
1. Those with direct or restricted exchange (generally marriage to the first or second cross-cousin category); direct exchange is widespread in Australia and the Amazonia.
2. Generalized exchange is another elementary structure. It is typically the marriage of males to the category of their matrilateral cross-cousins, notably seen in Asia. The caste system in India plays a role in promoting this type of marriage.
3. Individuals who follow delayed direct exchange is the next type. This marriage would come about due to males repeatedly marrying their patrilateral cross-cousins. For formal reasons, patrilateral marriage generates a delayed pattern where women go in one way in one generation and then back again in the next. Matrilateral marriage develops a pattern where men accept women in marriage from the same group as done by their fathers. Genuine patrilateral cross-cousin marriage with delayed direct exchange is not feasible and cannot be found anywhere as a stable form, among other reasons.