Al Villanueva was 12 when the 9/11 terrorist attacks on the World Trade Center prompted the U.S. to invade Afghanistan in 2001. Eighteen years, three tours of duty and five NFL seasons later, the war continues. Mr. Villanueva, the Steelers’ left tackle and locally perhaps the most well-known veteran of the war in Afghanistan, belongs to a large Pittsburgh community of post-9/11 veterans, a portion of the nearly 800,000 who have deployed to Afghanistan with the initial mission of hunting down Osama bin Laden and the Taliban who protected him. Bin Laden is dead, but the Taliban, once nearly vanquished,...