What is the theme in Ishi: Last of His Tribe by Theodora Kroeber?

Genocide is a central theme in "Ishi: Last of His Tribe", as it was the massive slaughter of Native Americans by the European settlers that led Ishi’s family into hiding. Ishi grows up among the seven remaining Yahi who have escaped the saldu, or white men, and have built the village of Tuliyani, hidden in the foothills of Mount Lassen. Ishi asks his Grandfather about the arrival of the saldu, whom Grandmother claims had come from within the mountain.