Hogwarts: Becoming the White Lord from Breathing - Chapter 34 Harry’s Christmas Gift

Killed by a Sage Emperor and reborn as his 13 year old self, Nie Li was given a second chance at life. A second chance to change everything and save his loved ones and his beloved city. He shall once again battle with the Sage Emperor to avenge his death and those of his beloved . With the vast knowledge of hundred years of life he accumulated in his previous life, wielding the strongest demon spirits, he shall reach the pinnacle of Martial Arts.

Known as the youngest academician-level senior engineer, Zhao Guoyang was reborn in the 1990s. In this era of economic globalization, with his extraordinary wisdom and extraordinary insights, he created one miracle after another and became a name that shocked the world!

Wisdom is condensed every bit, brilliance is created by sweat, and witness the rise of a great power!

- Description from novelbuddy

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.

The best way to declare war on a spy as an ordinary person is to become a spy as well.As a spy, if you want to go to war with a powerful espionage organization, join an equally powerful espionage organization.If you are unable to join any powerful espionage organization, then establish your own espionage organization and fight until destruction or victory.This is the war of spies, telling the story of how a group of ordinary people achieved extraordinary success.