MTL - Naruto’s Hidden Orphan - Chapter 231 Immortal Yin Xiang.

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.

In the residence of the Duke of Zhenguo, the legitimate young miss, known for her icy demeanor, had transformed overnight.She, who usually regarded no one, woke up to confront anyone she saw with a few harsh words, using her frail body to intimidate so much that no one dared to touch her.Afterwards, this legitimate young miss began taking on retainers, nurturing powerful officials, engaging in commerce, and recruiting troops… Every act so shocking and audacious, it defied the norms and provoked fear in all who spoke of her!Yan Wanqing was seen as an enchantress and a disaster by the people, a thorn in the flesh and a nail in the eye that the ministers wanted desperately removed, an entity everyone shunned as if she were a venomous snake.Only the Crown Prince Mingyue, descending from the divine altar, in the dark, godless alleys, grasped her neck and repeatedly asked her, “Will you marry me or not?”

One day every human on the world suddenly receives a mail claiming to enact the World Salvation Project. Half in doubt Kurosaki Shion, a diligent university student and loner, follows the mail’s instructions, becoming one of a million Demon Kings governing his very own Domain in the new world.

*** This is a post-apocalyptic story containing many fantasy elements. It is a somewhat dark tale following Shion as he grows while aiming for the unification of the all too sudden new world. It has many game-elements bolstered by strategical thinking while at the same time providing funny moments and romantic encounters.

Su Wan is a Realm Destroyer. She shuttles to different time-spaces using the identity of the “Cannon Fodder Ex-Girlfriend”, dedicated to plotting how to happily tear apart the male protagonist and the female protagonist. –There’s no such thing as protagonists who can’t be torn apart, only Ex-Girlfriends who don’t work hard enough~

- Description from Novelupdates