Hammenammir was originally played by Shadowbound, if you'd like to ask a few details of him. They're skilled strategists and planners, but at the same time possess many illogical traits and contradictions. In a sentence, their outlook on the world and their purpose in it could be characterized as: 'We must fight to redeem ourselves from a legacy of violence'.
Ysir have a distinct 'Victory at All Costs' mentality. For example, if you fight an enemy, who controls more of your homeworld than you do, while you possess stronger forces in space, it is considered a reasonable action to annihilate your own homeworld in order to give you a greater chance of emerging ahead of your opponent.
This may be an explanation for how the Ysir ended up as wanderers.
Anyway, I thought you'd be very interested, and they're one of the most cool, yet undeveloped species currently present in the NES.