Top military adviser Profr Sir Hew Strachan has criticised Britain's lack of "strategic thought" in its involvement in Iraq, Afghanistan and Syria.
In his upcoming book The Direction of War, Strachan condemns the way British and American governments utilised military force as they "bungled" their involvement in the conflicts.
He accused Britain of "strategic failure" - in which the lack of a definitive objective has led to the mishandling of expensive wars. He also said that there were no definitive long-term ends in both Britain and America's use of military force.
In the book he says:
The understanding and meaning of strategy has got lost, confused or become stripped of meaning. Without strategic thought our execution of war aims is inevitably bungled – we didn't know what to do or how we wanted to do it in Iraq and Afghanistan."
He also commented that David Cameron had a "seat-of-the-pants" approach in not delivering a British military intervention in Syria.
In August, the British government's motion to support military intervention was defeated 285 to 272, by a majority of 13 votes.
Sir Hew said: "The seat of the pants way [with insufficient preparing of the press or parliament] in which our approach to Syria was handled showed a total absence of strategic thought and is, almost, another case study in strategic failure."
Strachan criticises both David Cameron and Barack Obama for lack of coherence.
"This criticism applies equally to the UK and US. Presently we can't make up our minds in Syria.
"We cannot articulate how our use of military means would deliver on a political end.
"The problems both Obama and Cameron have had in Congress and in parliament have been indicative of the loose use and understanding of strategy."
Strachan is the professor of history of war at the University of Oxford. He advises the UK Defence Academy and sits on the Chief of the Defence Staff's Strategic Advisory Panel.