Final answer:
The phrase that best completes the diagram is 'Protecting citizens'.
Step-by-step explanation:
The phrase that best completes the diagram of the purposes of governments is Protecting citizens. Governments have a responsibility to ensure the safety and security of their citizens by protecting them from outside interference and threats.
This can be seen throughout history, such as the construction of the Great Wall of China by ancient Chinese emperors to defend their empire from attacks.