You might want to be a bit more specific in what you're looking for, and narrow the period by a lot. In 500 BC Rome was barely the most important city in central Italy; in 500 AD Rome was barely the most important city in central Italy - in between you've got the entire rise of the Rome, the conquests overseas, the crisis of the Republic, the founding of the Principate, the crisis of the third century, the Dominate, the split in West and East, and the fall (or transition) of the Western Roman Empire. And that's just the first part of your question.

Most of the people studying history study a particular period or topic, or a combination of period and topic. For instance I could tell you a lot about Roman magistrates in the period 218-133 BC. That's a very specific topic and a 85-year period. Many people will have something similar (with another topic and a different period). Compare that to what you're asking: three hugely broad topics and a 2000-year period. You can't reasonably expect an answer to that which meets the standards of this sub.

(Also, millennia is the plural form of millennium. So it's "one millenium".)