Smith's second involvement with the Balkans was in 1999 during the Kosovo War, when he was serving as NATO's Deputy Supreme Allied Commander Europe, overseeing air strikes against Serb targets.

Smith's thesis, and the central theme of The Utility of Force, is that the world entered a new paradigm of conflict at the end of the 20th and beginning of the 21st centuries, which he calls "war amongst the people", and that Western, industrialised armies are ill-suited to the new style of warfare.

The defining characteristics of "war amongst the people" are that conflicts tend to be timeless, more political in nature, and fought between parties that are part of, and in amongst, the civilian population rather than between uniformed armies on a battlefield.

It was compared favourably with Carl von Clausewitz's treatise On War and American reviewers felt that it contained important lessons for the United States military.

Nonetheless, reviewers praised Smith's analysis of modern war and recommended that The Utility of Force ought to be read by politicians and military officers.

He went on to serve as Assistant Chief of the Defence Staff for operations and security from 1992 to 1995, during which time he came to the conclusion that military force could only achieve one of four things when used to intervene in a political conflict: "ameliorate, contain, deter or coerce, and destroy".

[4] Smith was based in the Bosnian capital, Sarajevo, where he devised a strategy for the multi-national UN force that had been deployed effectively to carry out mainly humanitarian tasks but without a plan to bring the war to a successful conclusion.

NATO commenced air strikes against Serb forces led by Slobodan Milošević, again lacking defined objectives, while Smith worked to incorporate the bombing raids into an overall strategy.

[7] Smith discusses modern guerrilla and insurgency campaigns, including various civil wars and ethnic conflicts in the Balkans, the Middle East, and Africa.

[2] He points out that modern wars are rarely fought between individual nations, but the parties often consist of supranational coalitions or sub-state entities, and that Western governments in particular fight in such a way as to keep casualties and material losses to a minimum.

He believes that the commanders were working at a tactical rather than a strategic level, and that operations were not sufficiently guided by intelligence—relying too heavily on battlefield strength and assessments of the insurgents' technical capabilities, rather than their political objectives.

[6] William Grimes, writing in the New York Times, described The Utility of Force as "a closely argued, searching textbook on strategy and the efficient use of military power in the post–Cold War era".

Grimes also described it as a "difficult, challenging book", saying "you can almost hear the pointer hit the blackboard as he works his way rigorously through each argument and sub-arguments A, B and C, before proceeding to the next step.

Nonetheless, Ferguson concludes that The Utility of Force is "an impressive and absorbing work", and described Smith as "the Clausewitz of low-intensity conflict and peacekeeping operations".

[4] Academic Eliot A. Cohen, professor of strategic studies at Johns Hopkins University wrote for The Washington Post that the British Army had "a higher quotient of sophisticated leaders who have thought hard about the profession of arms" than was found in other armed forces, including the US military, which he believed explained why it "produces generals who write [...] serious, important books" such as the Utility of Force.

[5] Writing in the journal of the Royal United Services Institute (RUSI), Christopher Coker, professor of international relations at London School of Economics, gave a detailed analysis of Smith's opening sentence, "war no longer exists".

Nevertheless, Coker praises Smith for the latter's criticism of those who failed to recognise the shift in the paradigm of war, and of the lack of strategy in the military campaigns of the late 20th and early 21st centuries.

[3] In 2013, General David Richards, then Chief of the Defence Staff, included The Utility of Force on a list of publications that he recommended to officers wishing to improve their leadership skills.