My Multisystem In Isekai - Chapter 151 The Last One

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.

Bai Muchen had it all — not only was he the most renowned martial artist of the Nine Heaven continent, he even had the Five Meridians of Tianling and was engaged to Xuan Qingzhu, the beautiful daughter of his mentor. But everything falls apart when he’s set up by his fiancé and mentor during a cultivation session, and he is killed.

Reborn as a young man named Xiang Nan, the heir of a declining family, can Bai Muchen get his revenge?

[Ilyasviel completes the check-in and rewards himself for a height increase of 1cm]

Elijah: “???”

[Shizaki Kuangsan completes the task, rewarded with a historical video of Shizaki Kuangsan, please accept it! 】

Tokisaki Kurumi: “???”

[Fit Testrosa completes the quest and is rewarded with a whole set of bombardment flow for making friends with Takamachi Naiba! 】

Fett: “???”

[Shiroi Kuroko completes the task and rewards Misaka Mikoto Ai’s bento! 】

Shirai Kuroko: “…!!!”

Chu Chen silently watched the group of system hosts who had been playing with the system he created to the point of collapse, and drank tea very calmly.

“You don’t really blame me for the rewards you get. I’m only responsible for the system delivery system. You blame me for being like this…”

- Description from novelbuddy

After suddenly dying while trying to meet a deadline, Gu Huai transmigrated and became a non-human race.

This race is cruel and cold, making them feared and shunned by everyone in the interstellar world.

As the new king of the race and facing the group of parents who see him as a baby, Gu Huai said he was under a lot of pressure.

- Description from Novelupdates