Final answer:
The Nile River's ability to provide fertile soil through regular flooding made it possible for ancient civilizations to engage in agriculture, leading to the settlement's development in the Nile River Valley.
Step-by-step explanation:
The main reason for the development of settlement in the Nile River Valley during the New Stone Age was the Nile's ability to bring in fertile soil for farming. The Nile River is the longest river in the world, and it carries rich silt and nutrients from its upstream origins, which are deposited along its banks when it floods. This regular flooding created some of the most fertile land in the ancient world, ideal for agriculture and supporting the growth of civilizations like ancient Egypt and Nubia.
Moreover, the Nile River's reliable watering cycle enabled ancient Egyptians to plan for its inundations, which led to a stable and consistent food supply. This played a crucial role in the civilization's longevity and ability to support a large population. With agriculture as a stable foundation, Egypt developed intricate irrigation systems, advanced architecture, writing systems, and an array of cultural and societal advancements.