How borders are drawn and enforced has far-reaching consequences, whether we live on either side of them or halfway across the world.

Beijing has made an official complaint to the US following the controversial phone call between president-elect Donald Trump and Taiwan president Tsai Ing-wen that upended decades of diplomatic protocol, according to China’s foreign ministry.

In a statement issued today (link in Chinese), Geng Shuang, a ministry spokesperson, said that Beijing has “lodged solemn representations” with the US over the matter, which is akin to lodging a formal complaint:

We have noted the relevant reports and lodged solemn representations with the US’s relevant parties. It must be pointed out that there is only one China in the world and Taiwan is an inalienable part of China’s territory. The government of the People’s Republic of China is the sole legitimate government representing China. This is a fact that is generally recognized by the international community. The “One China” principle is the political foundation of Sino-US relations. We urge the US’s relevant parties to abide by the commitment to the “One China” policy and the three Sino-US joint communiqués, and carefully, appropriately deal with Taiwan-related issues to avoid unnecessary interference in Sino-US relations.

Yesterday, Trump accepted a congratulatory call from Taiwan’s Tsai. According to accounts of the call, he discussed strengthening bilateral ties with the island as well as increasing Taiwan’s international influence.

Taiwan has been self-governed since the end of the Chinese Civil War in 1949, but China views it a renegade province. Since the US recognized the Communist government in Beijing as China’s seat in 1979, no US president, or president-elect, has spoken directly to their Taiwan counterpart, at least publicly.

After Trump’s call, the White House said in a statement that its “One China” policy is unchanged. Earlier, China’s foreign minister Wang Yi said in an interview that the call was a “little trick” by Taiwan played on Trump.