Reborn with an Old Enemy on the Day of our Marriage - Chapter 17 - Love Mentality

After getting forcefully reincarnated into a world of an otome game he has no clue about, the protagonist is then killed and brought back to life by the prideful villainess with one desire.

To rule the world.

As the ruthless girl’s Eternal Servant, how will he dodge the fate that the game system has in store for him?

Because of his master’s wine, he had somehow become the husband of a cold CEO — I’m still a virgin, please be gentle. He was from an ancient sect and had both Buddhism and Dao cultivation methods. The youth Qin Wu stepped out of the great mountain once again, stirring up the winds and clouds in the city.

- Description from Novelupdates

5 years after the world changed, the final boss appeared.

The top five players in the world, including Specter Seo Jun-ho, finally defeated the Frost Queen…

But they fell into a deep slumber.

25 years passed.

“A second floor? It didn’t end when the Frost Queen died?

Specter awakes from his slumber.

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.