Sentence:  They differed in the balance they believed essential to the sovereignty of the citizen - but the supreme sacrifice each made served to <WSD>maintain</WSD> a still more fundamental truth : That individual life , liberty and happiness depend on a right balance between the two - and on the limitation of sovereignty , in all its aspects , which this involves . 
Meaning of the word marked with <WSD> tags:  keep in a certain state, position, or activity; e.g., "keep clean"