I’m Secretly Married to a Big Shot - Chapter 2969 - No Regret in This Lifetime

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.

A villainess known by all as a wicked woman who has done all sorts of evil deeds—Ducal Lady Violet.
She regained her memories of her previous life after she fell into a lake and almost died.
The very moment she woke up, she immediately visited her father, Duke Everett, and asked one thing.

“Please confine me to the annex.”

And so, she imprisoned herself there.
Now that Violet was secluded away from the world’s criticism and reproach,
She immersed herself in her previous life’s memories and started painting them.

“What the hell are you up to this time?”

Everyone was suspicious of just what she might be scheming.
However, the misunderstandings surrounding her gradually got resolved one at a time…

What would happen, if one day fantasy collides with reality?

- Description from Novelupdates

She is an ordinary leftover woman.

He is a young and influential person and would be the most powerful person in the city.

In the past, she had a love that was hard to forget, but in the end, it was not able to fight against reality and it ended in despair.

He had also been in a deep love but he was betrayed by his girlfriend and his friend and because of this, his marriage kept getting delayed.