No disrespect to my American friends but I think the reason the USA isn't shown clearly in the Bible is for the same reason Canada, Australia and New Zealand aren't. All these countries are populated for the most part by Europeans, so I think the Bible treats them as such. I also think it is because the USA has never invaded Israel.
The young lions could be a reference to the USA coming out of the British Empire, a lion being its national symbolic beast.
Anyways. If you are American, be glad your country isn't mentioned, because those that are will all wish they were not!