For the first time in American history, diesel fuel has crossed the $6-per-gallon threshold — a number that is less a data point than a signal. Driven by escalating tensions between Washington and Tehran that have begun to constrict the arteries of global oil supply, this milestone reminds us that geopolitical conflict rarely stays contained to the places where it begins. The price at the pump is, in this sense, a translation of distant confrontation into the language of everyday life.