I'm not qualified to answer your questions, but I can point you towards things that others wrote that may be able to.

Here's /u/Drylaw talking on Tenochtitlan, capital of the Aztecs, one of the largest cities in the world at the time of the Spanish Conquest

For the Andes, Chapter 7 of Terence N. D'Altroy's book goes fairly in-depth both on the scale and design of the Inca's capital.

As far as North America on cities, here's /u/Reedstilt talking about native urban centers.

There's certainly more to talk about regarding technological development, but this post from the FAQ is a good place to start.

I'd strongly recommend checking the FAQ or book list of the sub on these topics if you're interested in learning more.

When Europeans arrived in the Americas, no one was using rifles. Back in the early 1500s, arquebuses were cutting edge technology; rifles wouldn't come onto the scene until the 1800s.

In the grand scheme of things, gunpowder-based weaponry was a relative new phenomenon. Europeans started encountering such weapons during the Mongol invasions of the 1300s. The Muslim world encountered such weapons a little earlier, in the 1200s, also by way of the Mongols. The Mongols themselves got access to such weapons thanks to the Chinese, who had invented gunpowder a few centuries earlier. All gunpowder-based weaponry comes from those early Chinese experiments, which branched off of alchemists searching for new medicinal compounds and unexpectedly creating one that explodes.

With that in mind, it's not unusual that the people of the Americas didn't invent gunpowder. That invention was a one-off fluke that turned out to have useful military applications and spread over the centuries from its point of origin.

As for cities, there were several major population centers throughout the Americas. One of my older posts on the topic has already been linked here, but feel free to ask any follow-up questions.