Metztil's bellicose attitude towards others coveting his land clearly told Alexander that he was not only afraid of a fight, he welcomed it.
And when Alexander put himself in the man's position, the decision became easily clear.
He understood that Metztil was not being intentionally foolish nor was he hoarding land like a dragon would horde gold- just for the sake of it.
The fact was the Helvati were not only the strongest tribe now but was sure to get only stronger in the future.
So why should they compromise with their weaker counterparts?
The most logical action would be to take advantage of their position and gobble the others up, taking over their lands and turning them into slaves.
This was far better than to try and accommodate every one of the tribe's needs.
After all, even the legendary chief Coatl fell exactly because of this, he tried to please too many people and then inadvertently ended up antagonizing everyone.