FORT WORTH, Texas—Mattie Parker declared victory on Saturday as the next mayor of Fort Worth, Texas, keeping it one of America’s biggest cities with a GOP mayor. The 37-year-old Parker was in a runoff with Deborah Peoples, a former Democratic county chairwoman who was hoping to be the city’s first Black mayor. Parker has now become the youngest mayor of a major city. Peoples conceded defeat as Parker had more than 53 percent of the vote with ballots still being counted. “Today’s election was a pivotal moment. The entire country was watching,” Parker told supporters gathered at a west side bar Lola’s, Dallas News reported. “Because of your support here tonight, together we will do extraordinary things for Fort Worth, Texas. No. 1 is bringing our city together. Hear me and hear me well: We’re going to demonstrate that a world class-city is capable of being a premier destination. We …