British forces in Afghanistan have handed control of Nato's International Security Assistance Force to the US.
Nato troop numbers have risen under Gen Richards
Multi-national troop numbers have risen over the last nine months from 9,000 to more than 33,000.
They have been under the command of General David Richards, who has now finished his term.
His replacement, US General Dan McNeill, will have to deal with Taleban fighters who have taken control of the southern town of Musa Qala.
The UK withdrew from the town after a controversial peace deal with elders.
General Richards took over on 4 May 2006, with the Nato force responsible for Kabul and the relatively peaceful regions of northern and western Afghanistan.
He took the International Security Assistance Force (Isaf) into the lawless south for the first time and assumed command of many of the American forces in the east of the country from the US-led coalition.
But there has been some criticism from US quarters of the British policy of making peace deals with local elders.
General Richards said that Nato had just struck back in Musa Qala.
He said it was "almost 100% certain" that the leader of the Taleban grouping in Musa Qala "has just actually just been taken out in an air strike along with some of his leading henchmen".
He also said he was not disappointed that extra forces were only arriving now that he was leaving his post.
"I could have used them [extra forces] profitably last autumn.
"I think certainly in some parts of the south we would have removed the Taleban threat altogether.
"But I'm very pleased that General McNeill, my successor, will have them and I wish him the very best of luck."
The BBC's Alistair Leithead said Gen McNeill has been in Afghanistan before and will take over Isaf's mission of bringing security and development and helping to win over the people to the Afghan government.
There is an uncertainty as to whether he might take a more direct approach to the counter insurgency, our correspondent said.
Commanders have asked for further reinforcements to fight the insurgents, but so far only the US and Britain have pledged more troops.