Time Travel: I Am Invincible Against the Barbarians from All Directions

The great prosperity of the country, which ruled the land of ten states, hundreds of millions of people, and subdued the barbarians from all directions, now has frequent bandits inside and barbarians invading the borders outside. In order to revitalize this country, which is about to fall apart and the people are living in poverty, His Majesty even spent the money from the government. It sounds really sad. Although Chu An, as a young historian, came to this world inexplicably with the memories he retained from his previous life. However, when he saw the bandits and barbarians cruelly and trampling on the people and civilization like no end. He was determined to use what he had learned in his previous life to build an invincible and invincible army as well as the most powerful weapons, armor, firearms, artillery, etc. In every dynasty in history that he knew. If the enemy comes with barbarism, I will respond tenfold! Once it comes, it will be useful. In a word, drive out the Tartars and return our mountains and rivers! Otherwise, how can we rejuvenate the country? This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.