China is sending a strong warning to the Czech Republic after a politician visited Taiwan. China's Vice Foreign Minister Qin Gang urged the Czechs to observe the one-China principle, describing it as the foundation of ties between the two nations. This week, the Czech Senate Speaker led a delegation to the island designed to boost business links. China's Foreign Minister Wang Yi, currently in Europe, also called the visit a provocation. And one of his spokespersons echoed those warnings.