REIMS, France — They wear the same uniforms. They are around the same age. They occupy the same space on the field, literally the middle ground between those tasked with producing goals and those expected to prevent them. And none of them has been here before, not like this. Any number of superficial strands connect Julie Ertz, Lindsey Horan, Rose Lavelle and Sam Mewis, the four midfielders who top the United States depth chart and who competed for three starting positions throughout the buildup to this World Cup. But as the middle without which the entire U.S. effort on the field will crumble, the personal bonds that knit together their individual promise are anything but superficial. None of them know what it’s like to play in the midfield in a World Cup, but all of them know they aren’t alone. “I call them soul ties,” Ertz said. “Because I think when you have history with somebody your bond just is stronger.” The U.S. will play Thailand on Tuesday with a starting midfield that collectively lacks even one World Cup start in midfield. The front line is loaded with experience. The likely starters at forward — Tobin Heath, Alex Morg...