Sentence:  As an instrument of economic warfare, then, the "oil weapon" can be defined as the ability credibly to threaten to withhold the supply of oil from certain oil-importing nations in order <WSD>coercibly</WSD> to effect a change in their political stance. 
Meaning of the word marked with <WSD> tags:  Coercively; in a way that is coercive; by coercion.