Similar to Sir82, the world powers only count those that directly affected the Israelites, with 3 being named in Daniel. Rome and the "Anglo-American" world powers went on to affect Christians. There is a vast missing gap from Zenobia to Britain. JW's don't seem to care about the 2,000 year gap from Jesus to Russell, which they dismiss as the virgins sleeping.
I have some information touching on this at https://www.jwfacts.com/watchtower/blog/daniel-prophecy-history.php