Turkish tanks are lining up along Syria’s border and Recep Tayyip Erdogan is promising a new ground war – his fourth in six years in northern Syria. He is wagering that Russia and the US won’t stop him.Turkey began artillery, drone and air strikes inside Kurdish-controlled Syria nine days ago in retaliation for a bombing in Istanbul that killed six people. Erdogan has blamed that attack on Kurdish militants and ordered the offensive on an area controlled by the YPG (a Syrian Kurdish faction that controls much of the border region). Kurdish activists say that dozens of civilians have already been killed and non-military targets, including energy infrastructure, hit. Erdogan has vowed that the operation “will not be limited to an air war”.