Final answer:
The word 'integration' in the text indicates that barriers led to the unification of different cultural and ethnic groups in China, encouraging internal development rather than expansion through conquest.
Step-by-step explanation:
The word that helps you understand that barriers caused the people of China to become unified is 'integration'.
This term indicates that, instead of expanding through conquest, China focused on the blending or unification of different cultural and ethnic groups within the nation.
The historical context reveals that the physical barriers, such as the Great Wall and natural frontiers, encouraged internal development and cultural integration as opposed to imperial expansion.
This led to a state policy that promoted the assimilation of various cultures within China, fostering a unified Chinese identity over time.