The United Arab Emirates has secretly dispatched hundreds of Colombian mercenaries to Yemen to fight in that country’s raging conflict, adding a volatile new element in a complex proxy war. It is the first combat deployment for a foreign army that the Emirates has quietly built in the desert over the past five years, according to several people currently or formerly involved with the project. The program was once managed by a private company connected to Erik Prince, the founder of Blackwater Worldwide, but the people involved in the effort said that his role ended several years ago and that it has since been run by the Emirati military. The arrival in Yemen of 450 Latin American troops — among them are also Panamanian, Salvadoran and Chilean soldiers — adds to the chaotic stew of government armies, armed tribes, terrorist networks and Yemeni militias currently at war in the country. Earlier this year, a coalition of countries led by Saudi Arabia, including the United States, began a military campaign in Yemen against Houthi rebels who have pushed the Yemeni government out of the capital, Sana. It is also a glimpse into the future of war. Wealthy Arab nations, particularly Saudi Arabia, Qatar and the Emirates, have in recent years embraced a more aggressive military strategy throughout the Middle East, trying to rein in the chaos unleashed by the Arab revolutions that began in late 2010. But these countries wade into the new conflicts — whether in Yemen, Syria or Libya — with militaries that are unused to sustained warfare and populations with generally little interest in military service. “Mercenaries are an attractive option for rich countries who wish to wage war yet whose citizens may not want to fight,” said Sean McFate, a senior fellow at the Atlantic Council and author of “The Modern Mercenary.” “The private military industry is global now,” said Mr. McFate, adding that the United States essentially “legitimized” the industry with its heavy reliance on contractors in Iraq and Afghanistan over more than a decade of war. “Latin American mercenaries are a sign of what’s to come,” he said. The Colombian troops now in Yemen, handpicked from a brigade of some 1,800 Latin American soldiers training at an Emirati military base, were woken up in the middle of the night for their deployment to Yemen last month. They were ushered out of their barracks as their bunkmates continued sleeping, and were later issued dog tags and ranks in the Emirati military. Those left behind are now being trained to use grenade launchers and armored vehicles that Emirati troops are currently using in Yemen.