In the frontier era, the tomahawk was used more as a tool than a weapon, for the simple reason that a man in the forest needed kindling every day, but did not fight every day. Certain outlandishly wicked-looking designs sometimes seen in historical collections are not representative of what was ordinarily used and carried.
I got to thinking about this because the tomahawk is having a resurgence of popularity in our era. Some of the new designs are practical and some are, as in former times, less so. In essence, any tomahawk that is useful as a woodsman's tool can be used as a weapon, but the reverse is not always true. Indeed, not every tomahawk that is spiky and vicious looking is even a good weapon.
A tomahawk differs from a hiker's belt ax in that utility as a weapon was considered in designing the tomahawk, while the hiker's hatchet's potential usefulness as a weapon is incidental to its intended use as a chopping tool. This is often reflected in size and weight: A tomahawk is often lighter or longer than a camp hatchet. The length of the cutting edge is often less and the edge is generally more curved. One practical type of tomahawk has a spike or punch facing in the opposite direction from the chopping blade, similar to a fireman's ax.
Another style, popular in the old days because it was comfortable to carry thrust into one's belt, which a tomahawk with a spike on the back was not, has a simple hatchet blade and no extension on the other side, like so:
Many other variations exist, even one that includes a pipe bowl for smoking your tobacco. Others have hammers opposite their blades, similar to a carpenter's hatchet.
As to why the tomahawk is becoming popular today, I think what happened was that people realized that the heavy duty survival knife has its limitations. It is still just a knife; if you want more cutting power you need a paradigm shift. Fortunately the past provided a ready answer. Today tomahawks are being carried, as dual purpose tools and weapons, by some U.S. combat forces. As before, tomahawks get much more use as tools than weapons.
This model is popular with the troops. It is issued as part of a vehicular toolkit (the hatchet's National Stock Number is 4210-01-518-7244) and sometimes purchased privately. It has something of a history. It was designed by WWII Marine veteran Peter LaGana in 1966 and it saw some use in Vietnam--enraging some peaceniks, who are of course easily enraged. It is a simple and conservative adaptation of the spike tomahawk type. What is special about it is that there is nothing special about it. It is a reiteration of proven eighteenth century technology. Current production versions have composite handles, though LaGana's originals had wood handles. Other than that, the tomahawk in service today would not have looked out of place in a Minuteman's equipment.
So we have in the tomahawk a piece of frontier Americana that is still useful, though nearly every other piece of military equipment has changed radically in the mean time. It is a curious anachronism in that way, but if you regard it instead as the fully evolved form of a tool that already matches a useful set of tasks, and the tasks haven't changed much, then the tomahawk really doesn't need to change to keep up with the times.