Zero no Tsukaima - Volume 12 s2Chapter 1

A thousand-year dynasty would inevitably face decay, and a hundred-year noble family would eventually return to dust.What in this world could last forever?Was it an Immortal Body, tempered a thousand times, or the Martial Arts will, in Heart Unity with heaven and earth?Chen Mu came to this world, his sword in hand, and when he turned back at dusk, countless heroes and millennium-old Demons had all turned to dust, leaving only one person on the road paved with yellow sand.

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.

Carlos Valois thought dying once was enough—until he woke up as a 10-year-old in the world of “The Dark Era,” a game he'd mastered in his previous life.Born as the last heir of a fallen noble house, Carlos discovers he's destined for a tragic fate: in six years, he'll be manipulated into joining the dark forces and killed by his own childhood friend. But this time, he has the ultimate cheat code—memories of the future.While other kids play with toys, Carlos hunts for divine legacies. Using his game knowledge, he performs an ancient ritual and steals a Demigod Mark from the thousand-year Sacred Oak—a power that should have remained hidden for decades.At 15, Carlos awakens as a Death Herald with broken stats that shouldn't be possible. Most Death Heralds are fragile summoners hiding behind weak skeletons. But Carlos combines his necromancy with stolen divine abilities, creating a hybrid build that turns him into an unstoppable force......[Skeleton Warrior has successfully evolved into Purple Thornblade Skeleton Guard!][Purple Thornblade Skeleton Guard has activated Bond: Glory of the Purple Thornblades!][Twelve Purple Thornblade Guards have formed an Undead Armored Knight Legion!].....His skeleton warriors aren't cannon fodder—they're elite undead legions enhanced beyond normal limits through secret evolution paths that took thousands of players years to discover.Every “coincidental” encounter is actually Carlos farming legendary opportunities. While his sister thinks he's just a lucky genius, Carlos systematically raids every hidden treasure, secret technique, and forgotten legacy he remembers from the game. Ancient bloodlines, divine artifacts, mystical cultivation methods—if it exists, he's taking it.With his infinitely evolving undead legion, Carlos set out on a path to rewrite destiny and become the supreme Death Herald legend.

Monsters appear frequently, instances are everywhere!When various classes shine brightly, Li Haotian awakens to what everyone considers the most useless Illusion God class—the Mechanic!But what others don't know is that Li Haotian's Mechanic can unlock a special talent every ten levels![Unlimited Ammo]When others are cautiously navigating instances, Li Haotian is already surrounded by countless Superpower Mechanical creations—Gatling guns, Rocket Cannons, bombers, Wolverines, Terminators, intercontinental missiles, Aircraft Carriers...and, unlimited ammo![God's Eye View]While others are carefully exploring the enemy's situation, Li Haotian is eating hotpot and watching the enemy gradually fall into the encirclement of the superpower army, grinning.[Air Drop Support]When the enemy is playing outdated tactics like blitzkrieg and encircling points to reinforce, Li Haotian remains calm, pointing to the sky—the superpower army instantly descends thousands of miles away, covering the skies of Sakura Country!Abyss Dungeon, Slaughter Dungeon, large group instances, international war instances... Li Haotian sneers and goes alone.Because, I alone, can rival a million troops!