A lot of the COIN-conventional debate hinges around whether or not the United States Army can or cannot execute combined arms operations. Since the term as used in the debate can at times be rather nebulous, I thought I'd actually read a history of combined arms organization in the 20th century--and picked up Jonathan M. House's aptly titled Combined Arms Warfare in the Twentieth Century. Published in April 2001 (before 9/11, Iraq, and the genesis of the COIN debate), the book charts the evolution of combined arms organization from the late 19th century up to the present. The book ends with a short analysis of the reasons behind the Russian failure in Chechnya in 1995.
Despite House's focus on combined arms organization and competencies, the book does rehash a lot of history most students of conflict may have also read in books by Robert Citino, John A. English and Hew Strachan on European operations and tactics. That being said, the reader benefits from extensive tables of organization and equipment (TOEs) that House supplies for units of many different armies. House also covers the post-Cold War period extensively and ties it together to the more meaty (and familiar) tale of 1914-1945. There are also a lot of other subjects covered tangentially such as the evolution of armored fighting vehicles (AFVs) that tend to be slighted in books of this type. The problem of AFV design and infantry employment (both mounted and dismounted) is a crucial story that House tells very well.
House's main theoretical point is that the trend of combined arms warfare is the devolution of combined arms competencies lower and lower down the chain, with smaller and smaller units acquiring combined arms competencies, a point often echoed by Sven Ortmann. House sees the division as a necessity for the complexity of modern operations and a base for task-organizing more specialized groups of smaller units for specific tasks. He is very much a stickler for balance and points out through a dizzying variety of examples what happens when armies forget the need for organizational balance.
There is, however, nothing that would satisfy partisans in either the COINdinista or COINtra camp. House is very strong on competent organization and the need for combined arms skills but he does not talk very much in a prescriptive sense about the maintaining of those skills beyond chastising those who think that modern operations do not require combined arms.