Private military firms have been around for as long as history can date back. The idea of mercenaries were pretty much the only means of fighting back in the medieval and renaissance eras. The lack of a robust state infrastructure forced empires like Rome and Carthage to find a means of protection and security, paying soldiers solely to fight whether they are members of that specific empire or not. Coming out of the renaissance age, more structured states started to develop and the need for mercenaries rapidly declined. Even so, there are companies of this sort in today's society providing more means than just military executions.
The main motivating factor for these individuals involved in PMF's is profit, rather than political or social gain. When means of a conventional, state authorized army are unable to successfully protect or defend that state, other means such as PMF's come in as an added device at disposal. In today's modern society, there are different varieties for PMF services and different companies across the world.
A provider PMF is the most commonly known service, the direct military capability. A state or non state actor can hire a firm, give them the objective, and that company will carry out the task whether that be taking over land or killing a certain number of people. Next is the consultant PMF's, these companies are still very involved but not solely focused on the execution of other people. The main focus is the training and advice of local military forces hired by governments not located in the same area. The third option is support. This focuses on logistics and capabilities to carry out a task by other military means. These types of firms obtain the largest market amongst the three and can supply traditional armed forces with things such as food, ammo, and communication means from all over the world. So, are any of these means really necessary in today's world?
The world's political climate today has shown that nothing goes without notice of the public eye. Looking at past occurrences such as the vietnam war demonstrates how difficult it may be for office holders to send their troops into a war. These PMF's come into play as a backdoor option, no congress approval or nationwide backing is necessary to hire a private firm to achieve military objectives. Because of state and international laws, it is increasingly difficult for a conventional army to achieve an objective without many legal obstacles. PMF's are radically more capable of quickly and successfully achieving an objective than host militaries.
The cost of employing and paying an entire host military becomes much more expensive in the long run than it does when paying a PMF upfront. Each soldier must go through extensive, costly training before even being deployed into a war, then afterwards is compensated with health benefits, retirement funds, and other long term pensions. PMF's are already trained with experience and paid upfront with no required long term pensions after the job is done.
While soldiers are stationed all over the world, necessary means such as food, water, shelter, and avid communication is required to keep those bases functioning and properly running. Support PMF's such as MPRI solely focuses on providing all of these capabilities. The U.S Army uses these firms even today while soldiers are stationed internationally, and without them the bases would run out of resources and unable to function.