Tensei Ouji wa Renkinjutsushi to Nari Koukoku Suru

Reborn as the third prince of a tiny and insignificant country, Hero happens to learn the forbidden-yet-powerful art of alchemy. Combined with his knowledge from modern-day Japan, Hero's abilities grow beyond what anyone in his world could fathom! With his newly-acquired powers, he’ll bring his country back from the verge of extinction...! A combination of modern-day knowledge and alchemy to turn a weak little country into a prosperous nation!
The Reincarnated Prince Becomes an Alchemist and Brings Prosperity to His Country
転生王子は錬金術師となり興国する