By Mark Urban
BBC Newsnight diplomatic editor
Gen McKiernan did not sound like a man of the "Yes We Can" school
General David McKiernan's fall from grace is a salutary reminder of what is at stake for the US in Afghanistan.
US defence secretary Robert Gates dismissed him with some modern management speak about the need for "new thinking and new approaches".
But his departure after less than one year in the job has more of a feel of World War I or II about it, when generals were routinely "broken" or "came unstuck" in the febrile atmosphere of total war.
Gen McKiernan was widely respected for his intellect.
Having interviewed him shortly after the 2003 invasion of Iraq - the ground element of which he masterminded - I can attest to his soft spoken, cerebral presence.
But it also became clear, when my questions about the wisdom or otherwise of disbanding the Iraqi army visibly nettled him, that he was a man uncomfortable with press scrutiny.
Last year, someone who had seen the general in action in Kabul told me, "He doesn't get on well with Afghans".
His downbeat pronouncements about the progress of the military campaign had annoyed people in Washington too, where some regarded him as verging on the defeatist.
Gen McKiernan did not look or sound like a man of the "Yes We Can" school.
His fall reminds us that in the modern age, people who cannot get on with foreign leaders or get their media message across are simply unsuited to high command.
The US will now send General Stanley McChrystal to take over the command of its war in Afghanistan.
Gen McChrystal manages to combine the unlikely attributes of a smooth media operator - having been a Pentagon spokesman - with the fearsome battlefield reputation of being a key player in the secret world of special operations, turning the tide in Iraq.
Those who worked with Gen McChrystal as commander of Joint Special Operations Command (Jsoc), running America's elite counter-terrorist forces such as Delta Force, say he was like a soldier monk, taking just 10 days off a year and often accompanying his operators on "door kicking" raids in the worst parts of Iraq.
In 2005-6, when even many of the generals running the US war there seemed to be giving up hope, Gen McChrystal increased the pressure on al-Qaeda in Iraq and the Iranian-backed Special Groups.
Will Gen McChrystal apply his relentless, aggressive approach to Afghanistan? We will be watching out for the signs of any change in strategy or message.
The "Af-Pak battle space" is of course quite different to Iraq.
Gen McChrystal will already be calibrating just how different.