Final answer:
China's cultivators discovered rich fertile land, valuable resources, and adopted new agricultural techniques as they expanded, contributing to increased food production and economic growth.
Step-by-step explanation:
As China's cultivators expanded north and west, they found rich fertile land and valuable natural resources. The implementation of new agricultural techniques such as the use of chain-driven pumps for irrigation and the cultivation of quicker ripening rice strains that allowed for two harvests per year significantly increased food production and supported population growth. Additionally, the introduction of crops from the Americas like potatoes and maize enabled cultivation on less traditionally arable land, further increasing food production and leading to economic development.