I need help! So I read this Manga years ago and have no idea what the name is but it about...

I need help! So I read this Manga years ago and have no idea what the name is but it about a second or third prince of a nation that can communicate with the machines he creates. He always thought that his dad the king used them for the good of the people but turns out that he used them as weapons. Once he found out he went to complain to his dad since a war would break out and the king disowned him. He eventually leaved or gets kicked out and joins a caravan....or something. Fast forward a couple of years later and he had quite a few followers but now his dad or another nation is threatening for war and that's where I left off '_' he has a younger sister that loved him as a kid but now hates him for abandoning her in the castle. The art was nice but I can't find it and have looked everywhere I could for it. If anyone know please help °□° thank you!