Final answer:
Environmental Determinism is the theory that emphasizes the importance of integrating environmental factors and adapting to changes in the external environment.
Step-by-step explanation:
The theory that emphasizes the importance of integrating environmental factors and adapting to changes in the external environment is Environmental Determinism. According to this theory, human behavior and culture are primarily influenced by the physical environment in which they live. Environmental determinists believe that environmental conditions such as climate, topography, and natural resources shape human societies and their development.