Publius Flavius Vegetius Renatus, De Re Militari, probably 5th century CE:

We shall now explain the difference between the legions and the auxiliaries. The latter are hired corps of foreigners assembled from different parts of the Empire, made up of different numbers, without knowledge of one another or any tie of affection. Each nation has its own peculiar discipline, customs and manner of fighting. Little can be expected from forces so dissimilar in every respect, since it is one of the most essential points in military undertakings that the whole army should be put in motion and governed by one and the same order. But it is almost impossible for men to act in concert under such varying and unsettled circumstances. They are, however, when properly trained and disciplined, of material service and are always joined as light troops with the legions in the line. And though the legions do not place their principal dependence on them, yet they look on them as a very considerable addition to their strength.

Hm. From Miller-McCune, November 15, 2011:

More than 260,000 contractors were employed in Iraq and Afghanistan as of March 31, 2010…The dominant factor driving savings was the lower wages paid to local and third-country-national contractor employees. The report said that more than 80 percent of those employees were not U.S. citizens…Looming just as large in the report is the unprecedented demand for contractors. “We rely on contractors too heavily, manage them too loosely, and pay them too much,” former commissioner Dov Zakheim testified on Oct. 19 before the Senate Armed Services Subcommittee on Readiness. …The Defense Department simply can’t keep up, according to the report. Oversight has taken a backseat to expediency. “The number of Defense acquisition professionals had declined by 10 percent during a decade that saw contractual obligations triple,” the report states…Contractors represent U.S. policy during times of crisis and conflict and they are essential to wartime operations. Yet, while contractors now make up half the personnel in war zones, “The Defense Department has never treated oversight of contractors as a core function.”…What is more, the contractors control many of the levers of defense, and on that front, the Commission on Wartime Contracting was blunt: “National security is not a business decision.”

QED, or, perhaps, SPQR…