There Was No Secret Organization to Fight with the World's Darkness so I Made One (In Exasperation) - Chapter 24 part3

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.

"There is a thin line between poison and medicine, and I shall make you dance on it!"

This story tells the life of two people, a noble only in name and an older wife from the army, married through a tentative agreement. In the bone-chilling cold, they spend their time hunting, gutting, and cooking by the fireplace. Their daily life passes peacefully. This is the warm love story recounting their daily lives.

Sixty years after the global catastrophe, the Little Freeze Period ended, and the governments of the living regions began to collect land in the anarchic areas to be planned on a large scale, reorganized resources, and entered the recovery stage in an all-round way. These two decades are also called “golden Twenty years”.

This is a bright era in which new regions are rising one after another, politics is set up, capital is acting, careerists are everywhere, heroes are powerful, villains and grassroots are rising together! A young man rises up in troubled times with a full stomach of strategy, hides a tiger in his chest, and measures the world.

- Description from novelbuddy