Single Spell Sorcerer - Chapter 97: Encounter with the Iron Leopard

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.

He died on Earth with nothing—no legacy, no power, and no second chances... or so he thought.After getting hit by a truck, a disillusioned young man awakens in the body of a boy named Zane, in a war-torn fantasy world where nations clash over power, and magic is the law of survival. Gifted a mysterious book from parents he barely knew—and now lost forever—Zane accidentally awakens the Void System, a cold, cryptic force that offers power... at a price.In a world of monsters, systems, and bloodshed, Zane doesn’t get a choice.Survive, or vanish into nothing

What if Magic has always existed ever since the beginning of the Earth we are living on, but history has been written in order to hide these facts. What if the prosperous and well-known people in history is actually a mage?

Enter a magic academy, rule your country. Be at the pinnacle of life! Join me in the journey of Emery and the others in the world of Knights and Magic as he becomes the Earth's Greatest Magus.

Xia Yuqing is a shut-in+fujoshi from the 21st century. After an accident, she transmigrates into the body of a young princess forced into a political marriage to another country.

“W-where is all this blood coming from? Is this– Is this nose blood? AH, YOUR HIGHNESS! A-are you alright? What? No! You mustn’t! Princess Xia, please, come back!”

“… I… need… to… see…”

The aide could only helplessly look on as Princess Xia Yuqing crawled towards the emperor’s quarters, leaving a trail of blood in her wake.

Fujoshi: a term for a woman who enjoys reading about relationships between men.

- Description from Novelupdates