Written in 1897, The Abolition of Privateering and the Declaration of Paris is a superb resource when looking at the use of non-state forces by the state. Put simply, this provides period knowledge and perspective that is not available in later works.
More important is the information on the broad use, impact, and deep understanding of privatization by the nascent American government during the Revolution and the War of 1812, for example. During the Revolution, many towns came to depend on income from their privateers, such as Salem, Massachusetts. Their roving tactics that took them along the European and British coasts produced public diplomacy backlashes as they “came to be liked as little as their brethren of England.”
In 1812, when both political and financial capital were in short supply and with a navy outnumbered by almost 10 to 1, Congress granted the President the authority to “issue to private armed vessels of the United States commissions or letters of marquee and general reprisal, in such form as he shall think proper, and under the seal of the United States.” Congress, in granting the President this authority, gave specific instructions on compensation and, more importantly, monitoring the privateers as they were keenly aware of the impact on public diplomacy and foreign policy these raiders have.
In both cases, Congress made it clear that it would not and did not cede responsibility for war when they authorized the President to hire private vessels, and compensate them as privateers, but placed clear parameters on pay and, more importantly, monitoring.
This book is a hidden gem and is a font information on how privatization then is different than now. Further, it contributes to an understanding of why privatization went by the wayside.
This is on Mountainrunner's recommended reading list for privatizing war and a worthwhile purchase.