Surprise! Tyrant's Little Crybaby Went on a Killing Spree After Being Reborn - Chapter 609 - : Since You’re Obstinate, Go to Hell

With the Goddess’ blessing, he became a 『Divine Knight』 and founded an Empire.
As time passed, he grows older, and by the time the heavens called for him to come, the Goddess showed before him, asking for his last wish.

He wished to be reincarnated in the future.
He dedicated all his life for his people, he had no time to master his own arts.
This time, he wishes to live for himself, forging his body to the utmost limit.

The Goddess complied with his wish.
In the far future, the King shall reincarnate as the 『daughter』 of a renowned Knight family.
And, under some circumstances, she is labeled as a failure of a Knight, however——

「How convenient. I can stand on the foremost line without needing any rank. No better training than actual combat!」

Thus, the legend of the world’s strongest, most beautiful Knight Disciple (♀) has begun—

“She had just traveled through time and now she’s doing a cesarean on her dead mother? And the children were still alive! Then, she had barely had the time to relish in her joy before the stupid villagers were going to burn her as a witch? Later, an emperor arrived on his horse and said, “Come with me.” The girl asked, “Why?” He answered, “Help my precious horse deliver her foal!”

Lin Fuyin had only thought of leading a quiet life with her two siblings after avenging her mother. She had never thought of being embroiled in the murder within the royal family as a village girl! Follow Fuyin through her tempestuous journey and as she stands at the top of the Wei Kingdom! The phoenix flaps its wings, about to soar…”

- Description from Novelupdates

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.

Skyseal Emperor Gu Taxian is perhaps the greatest Emperor in all of history. He crushed the Hundred Empires and brought them to heel, built the vast Great Stone Wall to keep out the deadly wilders, relocated mountains and rivers to promote commerce, set up roads and highways, and even promoted free academies of learning for the common man in an attempt to uplift them. But the Skyseal Emperor’s ambitions involve more than just this – he is preparing to launch a great campaign to stamp out all pagan religions, wishing to allow all men to become like gods instead of merely worshiping them. Deities, demons, and immortals alike tremble and rage at the Skyseal Emperor’s ambitions.