Chinese officials are calling it a terrorist attack. Early this morning in the western city of Urumqi, 31 people were killed and at least 90 others injured when vehicles plowed into a crowded market and then exploded. It’s the latest in a series of attacks in China. In March, a knife attack by a group of men killed dozens in Southwest China, and just a few weeks ago, a bombing and knife attack at a train station in Urumqi, injured dozens more. China’s government have blamed the previous attacks on Uighur separatists — Uighurs are an ethnic Muslim minority who live in China’s vast Northwest region of Xinjiang, a Chinese province roughly the size of Alaska that borders Central Asia. China has so far not blamed any particular group for today’s attack.

Today’s attack comes a week after the trial runs for a line that will connect Xinjiang with the rest of China by high-speed rail for the first time. In the past, Xinjiang was always considered very far away from the rest of China — parts of it are closer to Baghdad than they are to Beijing and the people who live their have Caucasian facial features, many Uighurs don’t speak Chinese. But now a new train will reduce what was a trip that took days into hours, and that underscores China’s political control over this region, extending to economic control. Historically, Uighurs have always been businessmen — this is the home to the ancient silk route. But these days, many Uighurs are frustrated because they feel they’ve lost a lot of economic decision-making power over their homeland to people they consider outsiders from Eastern China who now dominate government and business there.