Kevin Costner’s epic traditional Western series started with Horizon: An American Saga – Chapter 1, but the Horizon movie explained little, instead using its ending to transition into Chapter 2. Driven by a talented and star-studded cast of characters headlined by Costner himself, the four planned movies of Horizon: An American Saga will explore the lives of multiple generations of settlers and Indigenous people as they struggle to carve out lives in the American West before, during, and after the Civil War. Chapter 1 introduced most of the major players and locations.
https://screenrant.com/horizon-an-american-saga-chapter-1-ending-explained/