Can someone please help me find a good thesis sentence about this book called The Cheerleaders by Kara Thomas, I need to write an essay and find the main topic and I'm quite unsure about what topic I should choose and write about

The details that best show evidence of tribal traditions are, "never in the history of his people had a man married a woman who spoke a different tongue” and "it has never been heard," was the verdict of an old man speaking a few weeks later.