World view:Kicking habits is hard, kicking 12,000-year-old ones a titanic trial. When our ancestors cracked the secrets of agriculture, and humans switched from nomadic to settled communities, taking, holding and defending land became vital. Some argue that military necessity was the raison-d'etre of our earliest forms of governance, writes Tony Kinsella.
The aggressive use of force in pursuit of political objectives formed a normal and integral element of governmental toolkits. Attempts to identify the elements determining success, or failure, in war pepper our intellectual records from the world's oldest recorded book - Sun Tzu's Art of War (6th century BCE) - to the present day.
Carl von Clausewitz, a Prussian soldier, offered his famous adage that "war is the continuation of politics with the admixture of other means" in his 1832 book On War. A rule-of-thumb that continues to inform political decisions.
Most armies excel at recording details of everything from how many litres of water 100 soldiers consume to the required ratio of medical to combat staff. Professional armies devote significant energy to analysing experiences in order to define rules. A central military question is that of governing conquered territories. How large must an occupation force be to securely hold, and effectively administer, a country?
The 1.6 million US troops in Nazi Germany when it surrendered in May 1945 gave a ratio of about one GI for every 15 German citizens. They deployed to secure every site of conceivable importance, and many that weren't. Once it became clear that there was no significant Nazi threat, US occupation forces shrank until the ratio became 1-to-40.
It is a calculation that varies according to the likely degree of hostility. Experts suggest a 1-to-25 soldier-to-civilian ratio for extremely hostile environments, ranging up to 1-to-70 for more benign situations.
When the White House began to consider attacking Iraq, the Pentagon reviewed its contingency plan (US Central Command OPLAN 1003-98) which called for up to 500,000 troops, or a solider-to-civilian ratio of 1-to-50. It was this reasoning which led the then army chief-of-staff, Eric Shinseki, to inform the Senate Armed Services Committee in February 2003 that "something in the order of several hundred thousand soldiers" would be required for post-war Iraq.
Shinseki's professional response cost him his job when the then secretary and deputy secretary of defence, Donald Rumsfeld and Paul Wolfowitz, publicly reprimanded him for being a "product of old thinking".
Their dismissal was partly based on the intellectual hubris of the Bush administration - that it knows better than the professionals. It was, however, primarily rooted in a toxic combination of ideological certainty and resource poverty. Neo-conservative theory triumphed over reality, particularly when that reality was that the US simply did not have enough troops.
The US, following President Bush's 2007 "surge", now has something in the region of 155,000 troops in Iraq. As the term surge suggests, this is a non-sustainable temporary maximum. The US commander in Iraq, Gen David Petraeus, acknowledged this reality at his Baghdad press conference on June 16th when he admitted that: "The fact is, frankly, that we have all that our country is going to provide us in terms of combat forces."
In the most benign situation, with a soldier-to-civilian ratio of 1-to-70, the US forces in Iraq would be capable of securing a country of just under 11 million people. Unfortunately today's Iraq is far from benign, and has a population of about 24 million.
There are two ways in which Washington might have been able to raise the necessary forces to have had any chance of succeeding in Iraq. One would have been to dramatically increase the size of its own armed forces. The other involved persuading other countries to supply 300,000 troops.
The first would have required the introduction of conscription in the US and the massive expenditure involved in drafting, equipping and training an additional 300,000 troops over several years. The absence of any clear threat from Saddam Hussein's Iraq made this politically impossible. This same absence of threat excluded any chance of a global consensus.
Washington lacked the resources necessary to execute its Iraq policy, a policy that was, and remains, so flawed that there is no hope of persuading either the US people or the rest of the world to supply the necessary forces.
The US is not only the most militarily powerful nation in the world, it is the most militarily powerful nation the world has ever known. While it is true that other countries such as China or India have larger armed forces, their ability to project those forces beyond their own frontiers is minimal.
Our most powerful nation has the capability, with its 155,000 deployable troops, to occupy a country of about 10 million.
The reality of these figures is that, given the absence of a classic conventional military threat, major military actions today are only possible on the basis of a global consensus - and the construction of such a consensus is only feasible when a clear threat presents itself.
Tony Kinsella is a commentator on international affairs. He lives in France.