Eternal life begins with saving my clan - Chapter 300: Conquering the state in one night:

By accident, Lu Zhiyu found the entrance to a low-dimensional world, and thus began a totally different journey!

Su Bai wakes up and finds that the world has changed drastically. He realizes he has come to a world of pets. After accepting the new setting, he is determined to become a powerful Pet Tamer.

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.

“Great Mr. Chen Yu, you were successfully elected as the leader of the human race last night. Is there anything you would like to say to the world?”Chen Yu, bewildered, woke up and hadn't even put on his clothes yet. He replied, “I have no idea, I just woke up...”