After Rebirth, the Celebrity Daughter is the Medical Expert! - Chapter 355 - 267: The Shi Family Sells Their House for Help (Ten Thousand Words)_4

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.

Jiang Xinyu transmigrates into the 1950s without parents. In a time of famine with nothing to eat?But she just wants to live the life of a happy-go-lucky slacker...So she has to roll up her sleeves and fight!Carrying space, full of blessings!Heaven's favor, what you think is what you get.While others starve, she gains weight, determined to live out the luck she didn't have in her previous life.

A world where waves of monsters descend every night...A world where only the strong can survive.Axel, a burned-out man from modern Earth, wakes up in a desolate wasteland with nothing but a strange “Harem Settlement System” with him.Given the power to build, command, and grow stronger, he sets off to carve out a safe haven in this broken world. But as his settlement grows, so does the number of beautiful and deadly women drawn under his blanket-ahem!-banner.Witness Axel's journey, rising to to the peak. From a simple, lone survivor to becoming the Wasteland Overlord. With the help of the loyal, dangerous, and irresistible thirsty harem girls!

“What kind of guardian would you want to be? the one who destroys everything or the one who protects everything?”

Jason, one of the many casualties during a nuclear explosion gets the chance to reincarnate into another world due to his deeds during the war.

He gets tossed to another world due to ending up with the Shadow god as his patron, something deemed impossible.

With a system to guide him in the world of Clover and a family jinxed through the generations, his adventurous life in new world begin.