America imposes a law unilaterally on another sovereign country and demands all other countries in the world abide by it.
In this particular case, the law imposed by the US is sanctions on Iran. Those sanctions were imposed because America says that Iran is a rogue country which is developing nuclear weapons that pose a threat to Israel, a US ally in the Middle East. But Iran had already halted development of nuclear weapons under a treaty made with the EU, China, Russia and the US during the Obama administration. Since none of these countries has followed the US in withdrawing from the treaty, they cannot be charged with breaking international law for continuing to trade with Iran.
If Iran pays the “protection fee” by buying US weapon and US treasury bonds, like the Saudis did, and agrees to sell its oil in petrodollars, perhaps America would not brand it a rogue state. But why should a sovereign country like Iran submit to the menaces and blackmail of the United States?
If Huawei has committed any commercial crime, the US should resort to international law and pursue the Chinese tech company as a legal entity, not kidnap a company employee in a manner only a barbaric state would resort to.