"Unprecedented". "Rare". "A watershed moment".
That is how some US media described China's latest move against US sanctions.

On May 2, China's Ministry of Commerce issued a blocking order prohibiting any recognition, enforcement, or compliance with US sanctions imposed on five Chinese companies over alleged Iran oil ties.

For years, US sanctions worked as a form of one-way pressure. What makes China's response significant is this: it changes the calculation. Third parties now face a new choice. Complying with US sanctions could also mean violating Chinese law and facing legal consequences in China.

China's response is not truly "unprecedented". Its determination to oppose unilateral sanctions, defend international law, and protect the legitimate rights of Chinese companies has always been entirely predictable.