Temperatures have been rising in the Taiwan Strait in recent months as the United States and Taiwan prepared to celebrate 40 years of the Taiwan Relations Act (TRA), a US law governing their unofficial relationship, on April 10. The latest incident was on the last day of March: Taiwan scrambled several fighter jets to intercept two Chinese warplanes that crossed a median line into Taiwan's airspace. This was the first time since 1999 that the Chinese military breached that line intentionally, according to Taiwanese media. The US State Department was critical, accusing Beijing of trying to change the status quo unilaterally and saying that such efforts were harmful and "do not contribute to regional stability".

But some analysts in Taiwan said the Chinese move was a warning to the US to stop sending warships on freedom of navigation missions to the Taiwan Strait. The US has done so on the 24th of every month since the new year, an act seen by the Chinese as provocative. Behind the tensions on the ground is also the strengthening of ties between the US and the self-ruled island, which Beijing regards as a breakaway province, as Sino-US ties have deteriorated. This can be seen in the tacit approval by the Trump administration last month to sell advanced fighter jets to Taiwan, the first time since 1992 that the US sold such aircraft to Taipei. Other moves that have boosted ties include two pieces of legislation last year: the National Defence Authorisation Act that calls for military ships to make port calls in Taiwan; and the Taiwan Travel Act that encourages senior-level civilian US officials to visit Taiwan, overturning strict bans on this. Some US senators have tabled a Bill, the Taiwan Assurance Act, that if passed will, among other things, step up military ties.