Re-Birth Of A Genius. Creator/Destroyer - Chapter 1: Sam

The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time.

After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is headed for destruction due to the acceleration of the Minus Concepts. To prevent this, negotiations must be undertaken with the survivors of the other parallel worlds so their 10 concepts can be released.

And so Sayama is caught up in the final battle to clean up after the Concept War which left behind so much enmity.

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 Pseudo-Holy Grail War of Snowfield is About to Begin!Moran, who has transmigrated into the Type-Moon universe, is determined to clear the game in one life!Waiting online, urgent!Ding! You have successfully activated the Life Simulator!• 【You drove out the foreign Olympian Machine Gods, took the hand of the Earth Mother Goddess, and founded a new nation and mythology.】• 【You are the Lord of the Millennium Castle, bestowed with the name Brunestud, and the beloved ruler of the land in the eyes of the Crimson Moon.】• 【You are the Final King of the Age of Gods, single-handedly preventing its decline and ensuring that Divine Age Britain endures to this day.】Behind this dazzling simulated life, Moran now faces—Arcueid: “Weren’t you supposed to pick me up at the Millennium Castle? Why are you here in the Holy Grail War?!”Artoria: “Enough! Come back to Britain with me!”Ereshkigal: “Moran! Who are all these women?!”As his ever-growing circle of admirers closes in, Moran realizes—This might just be the hardest “Kidney Grail War” in history.