Little more than a concrete pad with a beacon system, the Supply Drop Zone serves as the delivery point for a constant supply run that is requested upon its construction. USA cargo planes will provide a commander with a constant flow of $1800 worth of supplies every two minutes for as long as it exists. Unfortunately, it is not very well armored.
The United Nations, long having been plagued by corruption and bickering, serve little interest in the world today. During the Global War on Terror, the UN performed their last actions according to many people. Thousands of supply deliveries were cut off by GLA raids, peacekeepers were unable to contain the violence in Somalia and their delegate 'Blue Eagle' was even killed by car bombers while being protected by armed Humvees. The United States felt their time of glory was over and subsequently cut support to the organization under President Howard Paulson.
Lately, under Kevin O'Connor, the UN has regained their power in the Western world but solely to the continent of North America, where they stand as a sort-of 'secondary answer' to the North American Union, should things get real tight. They coordinate and help US forces in the field by sending in supply deliveries via airdrops, landing safely on US-secured drop zones coincidentally named Supply Drop Zones.