As the most famous vegetarians of the 20th century were Hitler, Mussolini, Stalin, Pol Pot and Gandhi, 
I think it would be safe to say that vegetarianism is a political movement.
 
Marvin Harris (the anthropologist) claims it was invented in areas of high population density to feed the population using fewer resources 
while simultaneously eliminating older less productive workers.
see:
 Harris, Marvin and Eric B. Ross, 
Food and Evolution: Toward a Theory of Human Food Habits. 
Philadelphia: Temple University Press, 1987. 
    Note especially Chapter 8 entitled 
    "The Preference for Animal Protein and Fat: A Cross-Cultural Survey" 
    written by H. Leon Abrams, Jr. 
_____, Cannibals and Kings: The Origins of Cultures. 
New York: Random House, 1977. 
     The story of how the needs of crop species forced man to become civilized. [See newer edition] 
_____,Good to Eat: Riddles of Food and Culture. 
New York: Simon & Schuster, 1998. 
 
Ray Audette
http://www.youtube.com/user/MrRayAudette