Outsourcing military operations is a trend that continues to grow. Most of these "mercenaries" are performing support jobs formerly performed by soldiers. There are over 10,000 of these working in Iraq for the American forces. The "temps" are cheaper, even though some of the civilians get paid more, for doing the same work, than the soldiers. But not always. The contractors that take on these outsourcing jobs are usually American or British firms, and an increasing number of their employees are from poor countries (Philippines, India) that have inexpensive, non-Moslem, English speaking skilled labor. In some cases, non-Americans are hired for political reasons. In Colombia, where the Department of Defense provides help in the war against the drug cartels. But Congress has limited personnel strength to 400 U.S. troops, and 400 U.S. civilian contractors. That has been gotten around by hiring non-American civilians (often ex-military Latin Americans) to help out.
There are plenty of skilled military people available for hire. In the U.S., most military personnel take advantage of the twenty year retirement system. This system was first introduced by the Romans two thousand years ago and used by many other nations since. But until recently, twenty years of military service left most men in no condition for further service. The 20th century changed that, with thousands of very experienced. highly trained and still physically fit soldiers retiring each year while still in their late 30s or early 40s. The pension isn't really enough to live on, and those retirees with experience in combat jobs don't have many other options to get top dollar for their skills. Many of these men go into security jobs, which have become more abundant since September 11, 2001. But there is also demand for highly skilled combat troops to help provide security for companies operating in rough parts of the world. This makes retired commandoes a hot commodity. But any retired soldier has lucrative opportunities for mercenary work. The American firm MPRI (which, aptly enough, stands for Military Professional Resources, Inc) was founded in 1988 to make use of these fit and highly skilled retirees. With a payroll of 2-3000, MPRI recruits heavily among recent retirees. But MPRIs troops are used only for training foreign armies and providing security, which is a growing business for mercenaries.
But security has long been a large industry, and has long attracted retired military personnel. The change in the last decade is the recruiting of elite combat troops for service as elite security personnel. In Britain, recent retirees from the SAS (British commandos) are in big demand. Such big demand that recruiters entice SAS men to resign (which is allowed in the British volunteer services) and double or triple their pay applying their skills to provide better security for large corporations.
Before it was shut down (for political, not legal, reasons) by the South African government, Executive Outcomes showed it was possible to quickly, and with few casualties, bring African type civil wars to a halt, and allow peacekeepers to get to work. Executive Outcomes recruited heavily among black and white veterans of the South African security forces. Many of these troops found themselves unemployed when the white minority gave up power in the early 1990s. So Executive Outcomes was able to hire men expert in dealing with African irregulars. This, understandably, made the new, black run South African government a little nervous. Many nations are fearful of highly professional, and effective, mercenary companies. The UN has condemned them, for many members see themselves as very vulnerable to a few hundred well trained mercenaries.
While the UN has long opposed mercenaries, more and more people in the UN are pointing out that the only inexpensive, and certain, solution to a lot of the nasty wars going on around the world is mercenaries. Not the undisciplined and rapacious mercenaries of old, but the small, well trained, led and highly effective organizations or former soldiers and commandos. The political hassles of getting UN members to provide less well trained and led troops wastes time and allows the killing to go on out in the many war zones that blight the planet. "Private armies" have never been popular, because they often become the basis for tyranny and warlord power. But the current crew of mercenaries consider themselves as another type of service corporation, and see themselves as working within the system. Just another form of security service, so to speak.
Highly professional mercenaries are nothing new. For thousands of years there have been highly professional mercenaries available. They have gone out of fashion in the last few centuries. But mercenaries have never disappeared from the scene for long, and it looks like they are coming back.