Skeleton Knight, in Another World - Chapter 13Volume 8 -

The world ended.Zombies and monsters rose. Cities crumbled.And Merek? He woke up in the apocalypse with a job that lets him create armor for lingering souls—spirits without bodies, desperate for purpose.Turns out, the dead don’t rest easy. Some are angry. Some vengeful. Others? Just lost. When Merek binds them into steel warframes, they don’t just fight... they evolve.Now, he leads a legion of the undead—ghosts in armor, bound to him by oath and fate.Faction leaders call him mad. Warlords want him dead. And God? If He’s watching, He’s not talking.Merek was supposed to die with everyone else.Instead, he got a support type job no one’s heard of... and a shot at rewriting his pathetic Earth-life.In this world, only the fittest survive.And Merek? He’s got undeads in steel at his side.

Pet shop owner Tang Wan was accidentally reborn into an interstellar world. When he opened his eyes, he found himself automatically married to a vegetable via the StarNetwork. A social status worth ten billion yuan; but with an unconscious husband, he was unable to withdraw any money. Tang Wan held the empty position of the First Gentleman, but was, in fact, a poor man.

In order to secure his future livelihood, Tang Wan was bound to the “Earth Pet System” and returned to his old business, with the goal of saving money, getting a divorce, and looking for a second spring!

After thousands of years of evolution, Earth’s energy depletion had long been abandoned to the distant corners of the Milky Way. All of the animals in the galaxy had evolved tremendously, and little furry cute ones only lived in textbooks. When Tang Wan and his cute little ones appeared, they became the treasures of the whole universe! The pet shop soon became famous in the interstellar world, and the whole universe lined up to be cat slaves~

Finally surviving past the compulsory marriage period, Tang Wan happily took off the diamond ring worth billions: he can finally sell it for money!

However, Tang Wan could never have imagined that when he sat down at the dining table on a blind date with some fresh meat, the vegetative partner that he had come to an agreement with would suddenly open his eyes.

Gong: I heard you sold your wedding ring for one billion yuan?

Tang Wan reached out and pushed him down on the bed: Open what eyes, quickly close them.

- 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.

[NO. 4212: ‘Humanity’ has failed the Demotion Match.] [NO. 4212: ‘Humanity’ has been deemed useless. Beginning deletion.] As Earth was being erased after their final game ended in failure, Martial Saint Sung JiHan managed to resist deletion and saw messages pop up in front of him. [To think someone would be able to resist being erased.] [Let’s give him an opportunity to re-challenge.] [Player ‘Sung JiHan’ is returning to the time of initial entry in The League.] When he woke back up, he had regressed back in time. Given a second chance, he swore to himself to stop the fall of Korea and humanity and take flawless vengeance against those that ruined things in his original timeline.

Follow the journey of Korea’s Martial Saint, Sung Jihan, as he struggles to prevent a future of destruction and ascends as the Martial God!