This is a short sum of how I think the naruto world links with our world
I think that the universe is the same as ours (besides the jutsu and stuff, different universal laws for that branch of stuff) but it took a turn at some point, probably before the 1900's. I now I'm probably wrong but I always imagine that Japan was never bombed and they never came out of isolation in the Naruto world. As there is a main land but no others specified, but they have some modern technology (at least to the point past the Industrial Revolution). The cities are also well developed as shown when Pain states that he wishes to control the world with Akatsuki.
After that part of the manga I kinda developed my own theory (AKA a bunch of crazy conspiracies). I think that maybe the higher ups in the land have set up a barrier jutsu (or technology) to keep the influences of the modern world out. It kind of reminds me of the Samurai purge that ended in the 19th century, the government was outlawing all things to do with Samurai (ie. carrying your sword in public) and the Samurai were shamed, many chose to rebel and die fighting to show their honor. I think maybe someone in the Naruto world chose to preserve the ways of the Ninja before the Modern world rendered them obsolete.
I think maybe Akatsuki's goal is to collect all the Bijuu and use them to overthrow the government and thus control the Ninja world by getting outside technology to make them invincible (In my theory the time that the story takes place isn't known, maybe it's 100's of years in the future and the outside world has created weapons that are incredibly strong). I also imagine that with the help of the Bijuu and the power of the individual Ninja of Akatsuki that they can conquer the modern world too.