Why does war remain...

...the so-called profession of kings? Why does war seem to be necessary for "glory?" What kind of glory is that? I am referring to the discussion I brought up in Cultural History on Friday... I cannot get past that whole "seeking glory through the agency of military conquest." Wouldn't a king be taking a huge gamble by embarking in warfare? I guess "glory" would only be achieved in the case of whopping success. Does that mean shame for failure in military pursuits? That just doesn't seem to make much sense to me, I suppose.