DxD: System of the Harem King - Chapter 170: Conquest

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.

He is high above, the mysterious and terrible King of the Wild. With one glance, he can see people’s romances. He hates women to the extreme, but at his first glance of her, he dotes on her and spoils her.
She is a humble transmigrator, a miracle doctor who doesn’t care for the many handsome men around her. She only wants to become strong, to be worthy of that god-like man. But when she’s finally sure of her feelings, she finds out she’s already been married for years…
……
When wronged：
She uses strength to hit the big handsome iceberg-like man in front of her eyes. “People say that I’m not good enough for you, but it is you who is an old cow eating tender grass!”
A man seizes the main point and laughs like an evildoer. “This husband has to eat the grass to confirm if it is tender or not!” He puts out the red candle……
……
The world says：
The barbarian king has no heart and has no passion.
A pregnant woman very miserably thinks,” If he has no passion, then who is responsible for this big belly?”

- Description from Novelupdates

Following the death of his popular online persona, seventeen-year-old Suzuki Mato decides it's time to retire from professional VR gaming. However, his plans are abruptly cut short when he's kidnapped from his high school and forced to be a guinea pig for Genaco Gaming, the world's largest esports and entertainment company. Armed with nothing but his wit and a new online persona, he's thrown headfirst into the virtual reality of “Live No Evil,” a VRMMORPG littered with overpowered bosses, secretive NPCs, and backstabbing gods. His mission? Find a way to conquer this new world and get back at the company that took over his life, all while avoiding 'Parallel' -- a condition that would make it impossible to separate his real and virtual personalities. Because in a world obsessed with VR gaming, Parallel means death, and Suzuki just doesn't have time for that...