The reason for war

Senzal Clan Territory.

Senzal and Kenzal clan territories were present right next to each other and they shared a common border. They both were such close rivals that whatever one had, the other would have something similar or same stuff.

For instance, Senzal Clan had Duram Tea Peak which brought in a major chunk of revenue for them annually. There was something similar in Kenzal Clan with the only difference being that they sold coffee instead of tea.

Senzal Clan had a Half Saint Rank army and Kenzal Clan had it as well. 

Kenzal Clan had three to five high level artifacts and Senzal Clan had around the same amount with them as well.

Both clans had a pretty similar population density. They even had a defense system that appeared as if one copied the other.