Love History Caused By Willful Negligence - Chapter 79Vol. 1 :

Arthur Ventrike, a genius second-year at the prestigious Wolkan Royal Academy, hailed to be the most talented in his generation, reaches the Swordsman stage of Knight at just 15 under Grandmaster Thorne Bladesong. But envy strikes when a fifth-year student tries to poison him. Though the plot fails, Arthur is left crippled, his dreams shattered. Just when all hope seems lost, he inherits a Great Sage’s legacy and sets out to become the greatest wizard along with the blessing of an indecent goddess and save the world from an ancient evil.

“Master, the people from the Zhuang family have come to cancel the engagement.”

“My fiancé whose beauty was said to be capable of causing the downfall of a city, finally decided to throw me away?”

“I think so.”

“I want to see this legendary beauty, and confirm whether this bastard is as really great as people said to have no flaws in all 360 degree, a picturesque appearance however you see him; does he need me to help him open the corner of his eyes (Epicanthoplasty) or reshape his chin (Genioplasty)?”

“Actually, he didn’t come.”

“He didn’t? He didn’t even come to cancel the engagement? What a wicked b***h.”

“He definitely will get karma.”

- Description from Novelupdates

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.

Sa Bina was on her way to write her SAT when she suddenly finds herself in a strange world. She is sent to be the old emperor’s concubine, but on their wedding night, the emperor gets murdered by no one other than his own son and the heir! To survive, Bina makes a deal with beautiful but deadly Lucretius and her life in this dangerous kingdom begins.