Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 17 - 17-15. At the Changing World

As part of the imperial family, every move by Chu Yuan in this game of chess is made with apprehension, fearing that with a moment of inattentiveness, the whole match will be lost in a single move.

Ascending to the throne at eighteen, not half a year passes before civil strife erupts in Yun Nan. Though the thoughts of the old guard at the imperial court are not exactly identical, they are all waiting to see how the new emperor will put an end to this.

Unexpectedly, before this side could make a move, a few thousand miles away, the King of Xi Nan, Duan Bai Yue, had already personally commanded troops to attack in all directions; not half a year had passed when peace was restored.

Sparse moonlight shines into the palace; Chu Yuan stamped the wax seal himself, and had a secret letter sent urgently to Yun Nan 800 miles away — this time, what must we(1) give in exchange?

Brush marks passed through the back of the paper; it almost can be seen, when writing this line, how angry the young emperor was.

Duan Bai Yue spread out a piece of paper unhurriedly, replying with only one word.

You.

Notes:
(1): Chu Yuan is using the royal ‘we’ here.

- 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.

The course of commitments never did run smooth.

The person that Pei Zhen hates most in his life is the perfect Fu Sichen. Alas, life is full of surprises and unpredictability. One fine day, an accident turns Pei Zhen into Fu Sichen’s pet cat! As Fu Sichen’s pet cat, he makes a shocking discovery about his sworn enemy – a deep dark secret that the perfect Fu Sichen has kept hidden for years. Trapped in his cat body, Pei Zhen moves from one adventure into another while trying hard to find a way of turning back into his human self. When he finally does, the world as he once knew, has become a completely different place!