21st century Goguryeo - Chapter 48

One day he suddenly found himself in hell.
All he had was the desire to live and a predation ability.
From the first to the ninth thousand circles of hell, he absorbed dozens, hundreds of thousands of demons.
Even the seven great dukes of hell bowed down before him.

– Why would you wish to go back? Doesn’t his highness have everything that’s in Hell?
– What do I have?

Nothing to eat, nothing to enjoy!
The only things in Hell are the barren lands and terrible demons!

“I’m going back.”

After ten thousand years he returns to Earth.

A scientific genius named Thomas Harrier was transmigrated to an imperial prince body after a car accident that took his life. He found out that he is in a world similar to our own with a timeline akin to early twentieth century. The body that he is occupying was the imperial prince of a failing empire who suddenly rose to power after a successful assassination attempt of his father. Unaware that the attack is just the beginning of what is to come. He faces many challenges throughout. Will Thomas Harrier be able to live his second life in peace while running an empire and getting it back to its former glory? Or will he succumb into a conspiracy lurking within the country's borders?

Expect some:

Cold war era techs.

Super battleship with advanced electronics, propulsion, and fire control systems?
Helicopters?
Missiles?
Modern medicines and equipment?
AC-130?
A nuke?
Challenger or Abrams or Leopard?
F-4 Phantom or MIG-21?
Colored TV's.

Everything!!!

PS. Cover not mine, I just found it on google.

“I believe that if you have a problem, we just need to solve it with firepower. If the problem isn't solved by then, it just means we weren't using enough firepower.”In a world of swords and magic, Lucen Thornehart, the eldest son of the Iron Duke, was considered the shame of the noble knight bloodline. No talent, weak, and worthless.Until one day, when a fever awoke his previous life's memories and the knowledge of the class from an old game he used to play, Gun Mage.More than just guns, he creates weapons that have never been created in this life and the last.A sword that heats up, turns crimson, and could melt metal.A rune-engraved gun that mages use to amplify their spells.A giant sword that you would only once see in a video game, which makes an explosion every time it hits an enemy.A gun that is powered by mana and shoots out condensed amounts of mana.Airships, steam trains, and boats.Lucen Thornehart isn’t here to play fair. He’s here to redefine warfare, with overwhelming firepower.

Kieran was just an ordinary part-timer — a high school dropout who had also given up on boxing. With no parents and no real family, he survived by working his ass off every day. He was raised by a man he believed to be his father, but later discovered he wasn't — though the man passed away before the truth could fully sink in. What Kieran didn’t know was that he was actually the sole heir to a powerful business empire, the hidden son of a wealthy tycoon.