Son-In-Law Lord: Start with a Black Iron Fortress

Chen Mo, a modern military designer, passed through his soul and became the son-in-law of an enemy country. At the beginning, he was treated as a "defeat gift" and given to the famous "Frost Valkyrie". The only dowry was a black iron fortress located on the border of death that was about to be breached by the orcs, and three thousand old, weak, sick and disabled people. Everyone was waiting to see his joke, even his Valkyrie wife was cold to him. But Chen Mo smiled: A fortress? This is obviously my eternal inheritance! While others are still fighting hand to hand with swords, a giant crossbow with a range of 800 meters has been set up on the top of my city; while the enemy is still worrying about food and grass, my terraces have been planted with high-yield potatoes; while the countries are still fighting among themselves, my black iron army has already arrived at the city!