This Ninja Is Obviously Not Strong but Really Hard to Kill - Chapter 66: The Masked Man Who Suddenly Appeared

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.

Cain was an ordinary boy who loved creative works, especially when it involved anime and games. Suddenly, he found himself in a strange space with an extraterrestrial creature, a cosmic horror called Bishop that he couldn’t explain in words besides scary.Given the authority of a King, he was tasked to create dungeons in the multiverse in order to change his future. He had been turned into the Dungeon Maker. The more known his dungeon was, the stronger he became!Rias: What are you? A Devil?Dante: Now, now. What are you? Wow, I drank too much. Look at her, a sexy devil.Zoro: Where am I? Is that a sea monster? Good, I will bring meat for Luffy.Helldiver: For Democracy!!!All worlds became connected due to the dungeon. However, don’t worry!Everything was under his control.

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.

It was the turn of the 20th century, and in the Philippine Islands, the fledgling Philippine Republic waited to be crushed by the overwhelming superiority of the American colonial forces.But John McClain, a U.S. Army veteran of the Korean and Vietnam Wars, dies and finds himself in the body of the governor of a remote Philippine province in the year 1898. Initially reluctant to take up arms against his former country and skeptical of the chances of success, he eventually decides to fight for the Republic.Now living his second life as Martín Lardizábal, politico-military governor of Marinduque and armed with modern military knowledge, he will change the course of the Philippine-American War.