Raised in Dungeon - Chapter 264 Clash of Justice and Prejudice

Thrown into a brutal world of swords and sorcery, his memories stolen by an unseen force, Magnus wanted only one thing: to go home.But every kingdom, devil, and god — along with regressors, possessors, and fellow reincarnators — seeks to carve him apart.Survival demands war. War demands survival.And with a System that hides more than it reveals, Magnus is dragged down a bloodstained path... one battle, one betrayal, one broken world at a time.

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.

I gave them my everything.My time… my strength… my heart.I trained while they slept.I smiled when they laughed.I stayed… even when it hurt.And what did I get?Nothing.They looked at me like I was pathetic.Like, I didn’t belong.Like I was… less.But I... the naive person I am, continued trusting them.They told me to act like trash, fine—I became trash.They told me to act like a scumbag, fine—I played the role.However...One mistake, one single moment...That’s all it took.And they threw me away.But now…Someone else woke up in my body.A stranger, a man who doesn’t know the pain I suffered, but wears my face.Let’s see what he does with it.Because me?I’m done with this life, so to the soul who took over my body...This is your mess now…'Gray'.

Jiang Shang travels through the Zongman world, but the first world is Fuyuki City?

Joan of Arc, who was not supposed to be alive, came to her door and begged him to participate in the Holy Grail War?

I thought it was the beginning of hell.

At the critical moment, the system awakens!

Just make choices, or rewrite the plot, to get amazing rewards!

“Ally with Joan, get: Top Heroic Spirit Template!”

“Choose to save Matou Sakura, get: Imaginary Space!”

“Summon a mad-ranked servant, get: the holy gun of the end!”

The Holy Grail War begins!

Facing the arrogant King of Heroes, Jiang Shang showed his magic whip under the dull gaze of all the heroes!

“Arrogant tyrants should be beaten constantly.”

“I won’t stop until you admit your mistake.”

- Description from novelbuddy