Afghanistan's southern rim, the Taliban's spiritual birthplace and the country's most violent region, has for the last two years been the domain of British, Canadian and Dutch soldiers. That's about to change. In what amounts to an Afghan version of the surge in Iraq, the US is preparing to pour at least 20,000 extra troops into the south, augmenting 12,500 NATO soldiers who have proved too few to cope with a Taliban insurgency that is fiercer than NATO leaders expected. New construction at Kandahar Air Field foreshadows the upcoming infusion of American power. Runways and housing are being built, along with two new US outposts in Taliban-held regions of Kandahar province. And in the past month the south has been the focus of visiting US and other dignitaries - Sen. John McCain, Defense Secretary Robert Gates, US congressional delegations and leaders from NATO headquarters in Europe.