I think it is one-piece, just not near the width of the blade itself.
If you look closely at the butt/pommel, you will se the rectangular size of the tang (pretty small). You can also see where it is "pinned" if looking on the rounded side of the butt itself.
While Ka-bar's have a rich & deserved combat history, I think knife making has evolved so much since WWII (i.e. blade steels, thicker tangs, grinds, handle composition, etc) that they may be a bit outdated to some.
That said, I've never been able to "kill" a Ka-bar and once a proper convex edge is added, they make for a good all-around slicer and a so-so chopper.
I say "so-so chopper" only because thel overall weight of the knife limits the amout of the blade's chopping efficiency; that's probably why Uncle Sam issued an Ontario made machete! ;)

