I Secretly Develop Myself In The Demon World - Chapter 556 - 298: Demonic Thought Crisis_2

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.

After breaking up with his girlfriend, he accidentally acquired a genius system and rose from there against the heavens, becoming invincible..

- Description from Novelupdates

Pei Jiu picked up a girl by the riverside. He settled her on the mountain, and planned to send her back once she recovered. This delicate girl was a useless crybaby, so Pei Jiu had to be a nice person. He cooked her food and washed her clothes. He let the troublesome girl ride on his shoulders so she could pick fruits. During winter, he would warm up the bed for her. One day, she hugged Pei Jiu’s arm with a smile. “Big Brother Pei, you’re really an honest and a good man. I will marry you and give birth to your babies!”

Pei Jiu eyed her critically and scathingly enumerated her shortcomings. She was ignorant and spoiled. She only knew how to pester and flirt with people all day long. Give birth to babies? Go ahead, give birth to caterpillars.

The delicate girl bawled so hard that she passed out. The next day, Pei Jiu returned to his mansion and told his servants to prepare for his wedding ceremony. When he returned to the mountain in the evening, Pei Jiu opened the door as usual, but he found that the cheeky girl had disappeared. He searched the whole mountain for her to no avail. No one would act like a spoiled brat in front of him anymore. What a headache.

Note : 娇 (jiāo) : tender/delicate/pampered/spoiled

- Description from Novelupdates

In an era where humanity has long conquered the stars, a girl with a restless heart yearns for more than the predictable comforts of galactic life—she wants to explore the cosmos for herself. But her dream is torn apart when she’s stranded on a forgotten planet, a dumping ground for criminals with no way out.Left to rot among the desperate and the damned, she stumbles upon a strange machine buried in the scrap heap of discarded tools by higher classed planets—one that fuses with her psyche and grants her access to a system unlike anything in known space. It doesn’t just guide her. It evolves with her. It builds. It changes everything.Now she’s on the run, pursued by the relentless interstellar police who want back what she stole. But with each escape, each discovery, and each battle, she pushes further into the unknown, reshaping the wreckage of the past into something new.Blending the inventive spirit of technical progression with the high-octane energy of cinematic battles, this is a story of survival, rebellion, and rebuilding—one shattered world at a time.