By far the most important of the treaty ports established after 1842 was Shanghai, where the vague extraterritoriality provisions of the various treaties were most sophisticatedly implemented. The two main courts judging extraterritorial cases were the Shanghai Mixed Court and the British Supreme Court for China. Similar courts were established for treaty countries, e.g. the United States Court for China. These had jurisdiction over the concession areas, which formally remained under Qing sovereignty. Initially, Chinese people who committed crimes in, say, the British zone, were remanded to Chinese authorities.