This Beast-Tamer is a Little Strange - Chapter 104 - : The Principles of Evolution

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.

Ian Percus, the second son of a countryside Viscountcy.

One day, he received a love letter from the future.

‘If we don’t protect the future, the world will perish.’

With an ominous warning scribbled by someone

Of the ancient gods only one remained in the world. This god lived alone for thousands of years and no longer had any desires. Legend had it that during the great war between the worlds he used his powers to turn the tide managing to seal the cataclysmic rift bringing order back into the three realms. Time flew by and hundreds of years passed in the blink of an eye.

In this time Shen Li was born into the demon world. Known as the Azure Sky King she was used to living a bright and dazzling life full of successes. Little did she know that her 1000th birthday would bring misfortune to her doorstep – a politically arranged marriage with her name on it. The Azure Sky King would henceforth marry the thirty-third grandson of the Heavenly Emperor, Fu Rongjun. This arranged marriage was meant to unite the Heavenly realm with the Demonic Realm, bringing the two together. Most would consider it good fortune to be related to the Emperor.

Unfortunately Fu Rongjun was infamous throughout the two realms for his Casanova personality. As the King who called the shots in the Demonic Realm, she had the ability to quell uprisings and end wars with a swing of her silver spear – there was absolutely no way she would marry such a flirtatious idiot. She had to escape from this marriage somehow even if it meant death!

In her escape Shen Li, never expected to meet a man that didn’t belong to any of the three realms. This oddball was truly strange!

- Description from Novelupdates