I have always pondered on the background of vegetarianism. At first I believed it was accountable to either spiritual or religious beliefs, where people didn't deem the slaughter of another animal or living thing as acceptable. The beginning of my investigations into vegetarianism discovered that customarily the action of abstaining from eating animals was undertaken by a variety of cultures and people from the beginning of civilizations.
Eastern civilisations appear to be the original influence from the world's oldest societies. It is my understanding that the removal of eating meat or killing animals was due to the cultural belief of reincarnation. Theravada, Hinduism and Buddhism are the main Eastern cultural teachings. There are a considerable number of other religious groups that encompass these religions, however, this is a broad overview.
As you are aware with Western ideals towards vegetarianism, different people have different views. The same applies to the Eastern cultures over history. Some of these cultures do in fact still consume meat, however, it is not the common practice and there are generally rules or guidelines based on its consumption.
The Classical and antiquity period, known for Greek philosopher Pythagoras, also provides some more recent insight into the history of vegetarianism. In order to study as Pythagoreans there was a requirement to abstain from eating meat. Again, this is due to the thoughts surrounding reincarnation of the human soul into animals. There are known parallels between Greek and Hindu philosophies and it is likely this aversion to the slaughter of animals based on reincarnation that was derived from these teachings.
During the Middle Ages and Renaissance period there began to be an increase in vegetarianism, limited however to minority groups. It wasn't until the 19th Century, that the United Kingdom and some other European countries founded the Vegetarian Society. As is common in Western Society, popularity can be a driving force behind cultural shifts, at that stage vegetarianism began to gain momentum.
The above is only a broad overview surrounding the history of vegetarianism. As mentioned before, each cultural identity holds it's own beliefs and adaptation in regards to the subject. At times is appears that drought, disease and other factors such as the shear expense of meat forced people to remove it from their diets.