Lady Lin’s First-ever Journey to Immortality - Chapter 504 - The Bewitching Lark

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.

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.

The Imperial Court of Tang Empire became dim and corrupt. The Emperor believed eunuchs. The officials vied with each other for authority. The Tang Empire was about to collapse. The flouring Confucianism, Buddhism and Taoism eyed it covetously. The three sects wanted to contend for the domination of the whole world. Which one would win in the end? Or would they coexist peacefully at last? Armies of different nations invaded the frontier on all sides. People and the whole world were in extreme misery. Who could save them?

A young man of the Imperial Clan was reborn in Chang’an. In the Last Life, he was framed and was driven out of his place. He was the king of the subjugated country. When he wandered on the streets, he wanted to be an ordinary people and live an ordinary life in Chang’an but failed.

In this life, he determined to fight against the heaven and change his own fate. He would not give those people an opportunity who framed him in his Last Life. He would hold his title and his place. In order to maintain order and peace of the world, he was going to wipe out all villains of the whole world with the Imperial Sword, adhere to the emperor’s principle, and enact the new national law. He would rule over the empire to prove himself.

- Description from Novelupdates

One day, a silver-haired goddess appeared before him.“Heaven-Defying Star. The one who goes against fate. The sole savior of a world doomed to end—”What the hell is this woman even talking about?“You must be the Regressor.”“… What?”No, I’m not.