I believe it is C. Hope this helps and give me branliest or failure.
Was a cause because building an empire needs manpower such as an army and a navy to conquer and keep the land that they colonised. The alliances system meant that a local conflict could easily result into an intimidating global one.
The correct answer is the first option.
It is in the unitary system and the unitary government that all of the key powers are in the hands of the central government. Under this system there is only one power that is the central government and any other administrative units have only so much power as the central government chooses and is willing to delegate.
