With respect to tribal societies, Fortes describes marriage as often having the aim of building or maintaining affinial alliances—even as being an “indespensible adjunct” to achieving that goal. He continues: “To adapt […] the most hackneyed of all sociological aphorisms, marriage could be briefly defined as the sanctioned movement from the filial status of son or daughter to the conjugal status of husband or wife.” Interestingly, however, for both these assertions to be true—that marriage is essential to alliance building, and that it involves a movement from filial to conjugal status—the filial identity must not evaporate entirely. While the conjugal status becomes dominant, the filial one must be preserved in a reduced capacity. This shared claim of a single person forms the basis of the alliance.
When marriage is used in this way, then, there is strong incentive to think about it in a manner that one could almost describe as tactical in nature. The status change of a single person can have profound and far-reaching political and economic implications. It can be used to herald peace between two previously conflicting groups, or to draw already-friendly groups into closer interaction. Trade, too, can function as a catalyst for, as well as a consequence of, similar group dynamics. One clear example of the ways these two forces intertwine is the strategic way in which French and English fur traders often followed standard inter-tribe politics seeking to marry high-status women when dealing with the matrilineally-organized Five Civilized Tribes. The political potency of a first marriage stabilized the terrain for trade relations; similarly, the trade relationship created a secure situation in which marriage was possible at all.
When viewed in this way, alliances resulting from marriage and trade bear a striking resemblance to those formed in times of war or rebellion. Ultimately, both can be analyzed from a rational-actor standpoint: the relevant actors act with an eye to benefitting their respective social and cultural groups. Tribes are brought together by way of clear-headed, strategic thinking.
However, this seeming similarity is not the end of the story. Alliances brought about by war may or may not survive the cessation of hostilities from the common enemy—or even before. Tecumseh’s American Indian Confederacy, for example, fell apart following his death. In such cases, tribes are brought together by an external force, rather than being propelled primarily by internal drivers.
Thus, we see that alliances derived from conflict with a third party can only occur in special circumstances. Alliances with their roots in marriage and trade, by contrast, are not only capable of forming in a wider variety of contexts, but are more stable, and can even be used to bolster alliances of the former sort.