Thousands of US Marines have plunged into Taliban controlled territory in the Helmand river valley. It’s the biggest military offensive launched under the Barack Obama presidency. It underscores Washington’s new strategy for Afghanistan.That strategy calls for the doubling of US forces there reaching some 68,000 by the end of the year. There is a total of 90,000 combined US and NATO troops currently in Afghanistan . Military commanders hope that by taking the valley in a powerful, lightning operation they can rout the Taliban from their strongholds and turn the tide of a stalemated war in time for the Afghan presidential election in August. There are thousands of Taliban fighters in their traditional strongholds in Helmand and nearby Kandahar. Those areas have been the source of the spreading insurgency in recent months. The region is mostly outside of government control. It produces the biggest share of Afghanistan’s poppy crop and accounts for 90 per cent of the world’s opium. US and NATO commanders are hopeful a rapid, decisive victory in the Helmand Valley will provide a turning point in the protracted war. The deeply entrenched Taliban have resisted previous attempts by the allies to oust them.