A key aspect of Circle of Days is the depiction of the formation of competing cultures across the Great Plain. While the people of the Great Plain live in the same geographic space, there is a vast difference between the cultures of the farmers, the herders, and the woodlanders, which sometimes brings them opportunities for cooperation, and at other times sets them against one another. 

Even smaller communities such as the miners have their own traditions and beliefs that are not shared by the entire community. They have their own private expertise of how to locate and dig a mine. When the mine is finished, they have rituals and prayers to offer thanks to the gods. Then, they take their flints to the gatherings, showing how this smaller community fits into the larger economic matrix of interlocking, co-existing communities of the Great Plain. The priestesses performs a social function. While they depend on the benevolence of others to donate food to them, the priestesses serve as a repository of knowledge for the people of the Great Plain, offering them not only spiritual guidance but an understanding of the calendar. The miners, the priestesses, and the larger communities all co-exist on the Great Plain, finding their own respective roles to play in the broader communal effort of existence.

The emergence of Troon as the Big Man of the farmers creates a situation in which the differences between the farmers and other cultures are almost too stark to co-exist. While the previous status quo relied on co-existence and community, Troon institutes on a fundamentally more selfish view of the world. For Troon, existence is a zero-sum game. His first significant act is to plow the Break, making farmland out of a stretch of ground that was reserved as a symbol of the co-existence between herders and farmers. Troon takes the land for himself and his people, meaning that the herders and their cattle no longer have easy access to the river. Troon does not care about the herders; he feels that he is competing against them, so anything that diminishes herders and helps farmers is good for him. Troon’s emergence and the threat of the drought combine to turn existence on the Great Plain into a competition between communities.

While Troon’s war is a stark illustration of the human cost of competition over cooperation, the plight of the woodlanders shows the human tragedy of Troon’s actions. The woodlanders are the most distinctive group on the Great Plain. They have their own language, meaning that—save those who are bilingual—their culture is somewhat alien to the other inhabitants of the Great Plain. They also live much more precarious lives, relying on sustenance and foraging rather than the raising of cattle or the growing of crops. In certain ways, the woodlanders are a throwback to an earlier stage in Neolithic civilization, one which the herders and farmers believe that they have outgrown. Amid Troon’s mounting violence and the accidental burning of the West Wood, the woodlanders are effectively punished for their way of life. Troon quickly plows their own territory into more fields, then kills their elderly and young ones when the woodlanders try to steal to support themselves. 

The tragedy of the woodlanders is that they do not survive long enough to witness the rebuilding of the Monument and the return to coexistence. Instead, their fate is to become a cautionary tale on the dangers of competition between cultures.