1. The problem asks how the phrase "the relationship deteriorated and within a few years the children of the people who ate together at the first Thanksgiving were killing one another" contributes to the author's purpose. 2. This phrase illustrates a dramatic change over time, showing that initial harmony between groups eventually turned into conflict. 3. The author uses this to emphasize the complexity and tragedy of historical relationships, highlighting that peaceful beginnings do not guarantee lasting peace. 4. By stating this, the author deepens the reader's understanding of the consequences of cultural clashes and broken relationships. 5. This supports the author's purpose of providing a realistic and nuanced view of history, rather than a simplistic or idealized one. Final answer: The phrase contributes by showing the deterioration of relationships over time, reinforcing the author's purpose to present a complex and realistic historical narrative.