Answer:
Oh I see it now, I didn't see it before. (Wifi slow)
Step-by-step explanation:
1. The global era increased drastically (I think that is how you spell it) probably because we have better improvement.
2. The semi-nomadic era stayed neutral for a long time.
3. The era of city-states started to figured things out. (I don't know what to put for number 3.)
I think that now that we have the technology, it helps us figure things out and we are way more advanced than we were years (YEARS) ago.
I wonder why the semi-nomadic era didn't increase till many years later because after that it started to increase slowly by a lot.