Intervention to protect endangered noncombatants during civil war is a frustrating enterprise. Sometimes no one intervenes. Or they are too late. Or extremely limited. Or the intervention backfires. Or after the interveners leave, the conflict reignites.

In her recent book, Andrea L. Everett focuses on another problem: when the details of an intervention imperfectly match what is needed. She labels this the “ambitions-resources” gap. Either the devoted resources are inadequate for the stated ambitions, or the ambitions are too modest considering the resources provided.

The book offers a plausible, if unsurprising, theory for this phenomenon: potential interveners sometimes feel pressure from bureaucrats or the public to take action, yet are concerned about potential dangers, so they employ risk-averse half-measures. Everett offers compelling quantitative evidence that half-hearted action is more likely when there is a combination of high pressure to intervene but an inhospitable conflict environment.

She then provides several case studies of such intervention—France in Rwanda, NATO in Kosovo, U.S.-supported African troops in Darfur—that confirm her theory. She juxtaposes these with two contrasting decisions by Australia in Indonesian civil conflicts—full-blown intervention in East Timor, but no action in Aceh&