Agoncillo's magnum opus, "The History of the Filipino People", was first published in 1960. At that time, the Philippines was still reeling from the aftermath of World War II, and the country was struggling to rebuild its economy, government, and society. The book was a pioneering work that aimed to provide a comprehensive and nuanced understanding of the Filipino people's experiences, from the pre-colonial period to the post-war era.

"The History of the Filipino People" by Teodoro A. Agoncillo is a seminal work that has shaped our understanding of Philippine history and culture. The book's comprehensive narrative, engaging style, and nuanced analysis have made it a classic in the field of Philippine studies.

The book was written during a period of significant social and cultural change in the Philippines. The country was transitioning from a colonial to a post-colonial society, and there was a growing recognition of the need to reclaim and reassert Filipino identity, culture, and history. Agoncillo's work was instrumental in shaping this narrative and providing a framework for understanding the complexities of Philippine history.

The third part of the book deals with the American colonial period, which lasted from 1898 to 1946. Agoncillo analyzes the impact of American colonialism on Philippine society, including the introduction of English as a medium of instruction, the development of modern infrastructure, and the exploitation of Philippine natural resources.