CF- Highly complex languages that many linguists say surpassed modern language in it's ability to convey thought and feeling much more precisely, for one. The pyramids, hanging gardens of Babylon, sailing around the globe, evidence of machines and possibly engines (Greece & Egypt), Underwater caves in Cozumel, Astronomical observations, philosophy that we still are amazed at. Most advance math had it's origins with ancient thinkers. Ancient American Civ's, Etc. Etc.
How can you say "God" didn't slow us down? The logistics of a language change would definitely hinder if not stop the accumulation of knowledge at least for awhile. As far as cities in Nimrod's day, they weren't cities like a modern American city. Probably just big camps. Reference to ancients with nukes, is merely hypothetical ( a "what if" if you will), what I read acutally ref'd having computers or nukes. It's not important. Just do the math time line in reverse (remembering that humanity and technology grows exponentially) but technology really booms once there is a common medium (English / Internet etc.) for it to be stored in. For example a Chinaman could have invented penicillin long before Pasteur, yet being remote and "un-published", didn't get credit and wasn't able to influence most of mankind with his discovery, it couldn't be put to use and built upon- understand?
If there are no mysteries of the ancients than why a field of archaeology and anthropology? National Geographic writes about half of it's articles on "mysterious" stuff from the past. Unexplainable many times.
Maybe I'm not expressing myself properly- sometimes writing brief (deep) responses is difficult for me.