The World Bank study found that while rebels may have strongly held political reasons to start conflict, the money gleaned from looting primary commodities is what makes guerrillas financially viable. "Diamonds are a guerrilla's best friend," said Paul Collier, author of the study "Economic Causes of Civil Conflict and their Implications for Policy." The report found that countries with little reliance on the exports of commodities, like coffee or diamonds, were relatively safe from internal conflict while nations that rely heavily on such exports are highly dangerous.