WITH FOREIGN competitors such as Facebook and Google blocked, domestic tech giants have for two decades dominated the Chinese market. The Communist Party has kept a firm grip on politics, but the tech firms have had considerable leeway in their business activities. “It was a Wild West within an authoritarian system,” says Martin Chorzempa of the Peterson Institute, an American think-tank.Now the Communist Party is reminding internet billionaires who is boss. President Xi Jinping has authorised an extraordinary crackdown. Last year the planned IPO of Ant Group, a giant internet finance company, was halted at the last moment. In …