In the kingdom full of happiness and love have been attacked by the Uchiha Kingdom for their beautiful lands and valuables. The attacked kingdom has been crushed and left to dust.
After the war, the Uchiha Kingdom are so angered to figure that the kingdom has no valuables at all, nor a beautiful kingdom at that! What the Uchiha's didn't know was that the Uzumaki Kingdom has married to a small village named the Namikaze Village. What they didnt know is that the Namikaze's swore to have their revenge if they go into war with the Uchiha Kingdom.
Years later, the Uzumaki Kingdom was long forgotten, but not for the Namikaze's. The Uchiha Kingdom's king fell ill and the heir took the thrown. Sadly, the new king was colder than the previous. The new king still remembers the war with the Uzumaki and how they still didn't take their prize. He also found the new kingdom, the Namikaze kingdom.
The new king finds that the kingdom has Uzumaki's, which lead him to believe that the two kingdoms are allies, meaning that the Namikaze Kingdom has riches and land. He decided to take action, so he orders an attack toward the Namikaze Kingdom.
The Namikaze's fought until there's a handful left and surrounded by the Uchiha's. As the new king sat on his thrown, soldiers came in and presented the King and Prince of the Namikaze Kingdom; the Uchiha's won the war.
The King found an interest towards the prince of Namikaze's, so he made him his personal servant. The King of the no longer standing Namikaze Kingdom is then sent to the dungeons for the rest of his life.
The Prince of the Namikaze Kingdom hated the treatment he was getting from the Uchiha Kingdom's king. He was humiliated and used. The Prince decided that he'll take matters in his own hands; his new goals are to assassinate the king to set his people free and revive the Uzumaki and Namikaze Kingdoms.