The US is not mentioned because it didn’t exist at the time plus it’s all about Israel and the “world” as it existed then which was Roman controlled. OTOH the US is the only country that protects Israel. Once the US is neutralized Israel’s enemies can attack her. Then Biblical prophecy comes into play. Just my thoughts.
There are lots of things in Bible prophecy that didn’t exist when it was written. There are also lots of things in the Bible that mankind did NOT know about when it was written, indicating God’s inspiration—things such as rivers in the oceans (currents), the 7 stars that comprise the Pleides (only 6 could be seen until telescopes came along).