Armed external intervention may sometimes be required to halt barbaric attacks on the vulnerable, but rebuilding political, economic and social order in the aftermath of an intervention is fraught with difficulty. Post-intervention problems may include coping with new and fractious actors, managing complex processes of change, addressing fundamental questions of political philosophy, coping with ‘spoilers’ and low levels of trust, and avoiding inadvertent damage to the intervention’s beneficiaries – all in situations where resources may be scarce and intervening powers at odds with each other. Interveners should strive to absorb the lessons of past interventions and master the complexities of the territory on which they propose to act. Patience and humility are sterling qualities in an intervening force, even where robust action is required. Adapting Montesquieu’s advice, if one must intervene, one should do so with a trembling hand.