Shannon O’Neil

In 2002, strife-torn Colombia took a bold step that paved the way for vastly improved public safety. Now Mexico is struggling to subdue drug wars that have killed almost 40,000 people during President Felipe Calderon’s tenure. It’s time to try the Colombian remedy.

Yesterday Mexico’s microfinance group Compartamos, backed by Accion International and the IFC, went public on the Mexico stock exchange. Where once only the largest companies and wealthiest elites had access,...