Imperialism transposed a social value that operates in economics (‘more is better’ as it pertains to wealth) to a social value that operates in politics (‘more is better’ as it pertains to power).
In economics, one could reasonably argue, the end state of the economic system is the consumption of the goods and services the system produces. The production (of wealth) is for the sake of consumption. In politics, the end state of the political system is the sustenance of political bodies. More is not better in politics; longer and more stable is better. The production (of power) is for the sake of resiliency and sustainability, not more power.
The legitimate objective of the political system is law, which implies the use of power under the rule of self-restraint. As soon as we introduce self-restraint into the equation we disqualify the value of ‘more is better’ as the basic motivator of the system.
Empire uses power for the sake of building resilient and sustainable political systems; imperialism uses power for the sake of more power.