An unified empire provide stability to the people. This could be traced back to 221 BC where China was unified into empire called the Qin dynasty.
The main reason is that chances of potential wars to be fought will be lesser and not that it implies there is no war whatsoever. Qin Shi Huang helped to remove this potential wars by unifying many states into one, by having an established centralized empire. Therefore, eliminate these states attacking one another.
The second reason is establishes a centralized system of government. This will enable a stable economy and highly structured political system. This will mean that the country will function like a large free trade zone within the empire. Where people can import and export without the worry of taxes being imposed on them, when entering city-states. Implementation of rules and laws will be simpler as it will be standardized throughout the land.
By having an empire, means having a common identity. Hence, war can be avoided; laws will be standardized and form a free trade zone.
Potential wars to be fought will be lesser meaning no chance or war occurring
Qin Shi Huang helped to remove this potential wars by unifying many states into one,
Eliminate these states attacking one another.
Centralized system of government.
This will enable a stable economy and highly structured political system.
Free trade zone
Import and export without the worry of taxes being imposed on them, when entering city-states.
Implementation of rules and laws will be simpler as it will be standardized throughout the land.