I Have Become A Demon God. Did You Just Ask Me To Be A Minor Villain? - Chapter 16: Got it! Talk to the Demon God!

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.

Beneath the peaceful façade of the modern world, an undercurrent of shocking crimes roils in the underbelly of society.

The spring fountain town of miracle that heals anything, Polka. In the hometown of memories, with my dear parents, there was a figure of a half-elf girl who swore to become my female slave.

Repeating such a memorable talk every time he drinks alcohol, 25 years old Andy Smeyson is a former blacksmith’s apprentice and an innocent crossbow soldier. Andy is surrounded by nice companions and competent and sexy bosses, which is different from what he had thought when he was a child, but this was a cozy life. When the half-elf girl suddenly appeared in front of him, he will jump into a furious destiny. Andy, who is weak but courageous​ and clever will meet a lot of different race ladies such as elves, half elves, dark elves, loli dwarves, dragon girls, beast girls and make them his female slaves one after another. The horny adventure started from a half elf girl who doesn’t stop liking him will eventually become a legend ──.

Born of a great family, world shaking genius.

The man who had shaken the world.

The story of the Swordmeister.