The most striking—though not surprising—thing about this graph is the much higher rate of homicides that involve a firearm, and also the dramatic variation in gun homicides since the mid-1970s. Guns are quite lethal, of course, but they also appear to be sensitive to other factors. For example, during the crack epidemic years of 1984-1989, homicides more than doubled among young black men, which may be a partial explanation for the spike during those years shown here.
The only other weapon that shows any degree of variation is the decline in popularity of cutting/stabbing. Today this weapon is responsible for fewer than half the number homicides as in 1980.
(Posted March 14, 2016. Additional text added on March 27, 2016.)