One Piece: From the Rocks Era to King of the World - Chapter 435 - : Akainu and Aramaki’s Death

In the past, the giants of the heavens and the gods were destroyed after the reincarnation of the world! Cruel curse, eternal hatred, Tan Yun is determined to never sink again! For the sake of loved ones and relatives, from now on, step on the corpse of the enemy step by step to surpass the peak! Defying the sky, killing all worlds, I am the only one!

- Description from novelbuddy

He was the scion cast aside by a powerful family, and he had hoped to return to a peaceful life in the city, but unexpectedly, trouble arose once more!

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.

At eighteen, her mother died in a car accident, leaving her all alone in the world. One day, her kindness in rescuing someone led to a life-changing transformation.She was provided with food and accommodation, and someone even arranged for “360-degree personal protection” for her!Just when she thought she had picked up a pie from the sky, she was tied up and sent to a training camp, embarking on a tough yet passionate new journey.Bully her? With Taekwondo, she'll beat you until you can't tell north from south!Compete with her in sniping? Rookies, step aside, she's challenging the strongest sniper!Doubt her hacking skills? Come on, sister will show you what playing with computers is all about!She stood out in the camp with high profile, top in every category, who would dare compete against her?Back home, the little overlord turned into a docile rabbit, utterly bewitching someone!Unable to endure it any longer, he dragged the little overlord to the civil affairs office and registered their marriage.At night, he returned home, and righteously set about 'educating' her!