A record 115,000 U.N. peacekeepers are now deployed in 20 countries, and their mission is more vital than ever. But critics and insiders alike are openly worried that the current peacekeeping model is overstretched -- and at risk of failure. NOW travels to the Democratic Republic of the Congo to witness today's largest and most expensive peacekeeping operation. There, 17,000 U.N. troops are tasked with protecting millions of people over a rugged and dangerous territory the size of the Eastern United States. But the effort is struggling -- last November, local rebels massacred civilians less than a mile from one of the U.N. bases.