The USA has more aircraft carriers and other modern weapons than the rest of the world combined. The USA has a highly trained military with lots of recent combat experience. The last time anyone in China had combat experience was nearly 50 years ago, and that was a tiny fight against Vietnam. The last major fighting was 70+ years ago, so no one is left from that.
That would be impressive alone, but remember that when I say the rest of the world combined, I am including a huge number of close allies in there. China has no close allies. Iran's close allies are guerrilla forces.