The evidence reviewed by political scientist Timo Kivimäki indicates that the “protection wars [fought by ‘coalitions of the willing’] have become the main source of violence in the world, occasionally contributing over 50% of total conflict fatalities.”
Furthermore, in many of these cases, including Syria, as he reviews, there were opportunities for diplomatic settlement that were ignored.
That has also been true in other horrific situations, including the Balkans in the early 1990s, the first Gulf War, and of course the Indochina wars, the worst crime since World War II.
In the case of Iraq the question does not even arise. There surely are some lessons here.