Orc Hero Story - Discovery Chronicles (Orc Eroica) - Chapter 13.5: The Great Eagle's Nest

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.

A world where the [Demon King] was defeated by a [Hero] that came from another world. People carelessly forgot about their fear of the [Demon King] and of monsters, living in peace.

In a forgotten and run-down cave in the mountains, a new monster that should not have been born was given birth.

The monster’s name was the [Black Ooze]. It was nothing exceptional other than its black color, an ordinary slime.

However, this slime had the special characteristic of being able to take the abilities of the living things it swallowed. It preyed on an insect that had paralytic poison, as well as other animals. Following that, it attacked a human, obtaining his knowledge and [Desire].

Before long, the monster established its target as the female mage that came to explore the cave.

This world still wasn’t aware.

At the feast of the Gluttonous House’s auction, there was a little girl with an exceptional furnace constitution for offer at a sky-high price. Everyone wanted to lay their hands on her. Suddenly, the little girl in the golden cage opened her eyes, radiating a cold gaze. She was no longer cowardly.

She was the gold medal assassin of the 21st century, transmigrating to become the good-for-nothing humiliation that everyone bullied, third miss Nalan Hexi of the genius doctor’s manor.

Meridians completely crippled, no innate skill to cultivate? What is she afraid of? She is the exceptional miracle doctor, and these injuries were nothing in her eyes.

Father doesn’t dote on her, mother doesn’t love her, everyone schemes against her? Humph, an alternate dimension in hand and an invincible spirit pet as well, she can destroy the small Nalan Manor with a flip of her hand!

Ugly complexion, malnourished and sickly in appearance, no one wants her? She recovered her unparalleled looks with the blink of an eye and gained a dozen good looking men as bodyguards!

That overbearing man who’d been sticking to her since the auction. Who said I was destined to be yours? I am my own, no one can decide my future!

A certain man: Then I am yours, will that do?

- Description from Novelupdates

Some people begin their lives with the odds in their favor but end up failing miserably.

Lin Jingzhe, having suffered many losses and setbacks, returned to his eighteen-year-old self just before failing his college entrance exam.

Business opportunities were everywhere in the early 1990s when the Chinese economy started taking off.

Now, this golden age would be his.

- Description from Novelupdates