I have become a vegan, but not completely.  I have a lot to learn
It dates back to its  roots in the civilizations of ancient India and ancient Greece.
Why did the people stop eating meat?
History of vegetarianism
The earliest records of vegetarianism as a concept and practice amongst a significant number of people are from ancient India and the ancient Greek civilizations in southern Italy and Greece. In both instances, the diet was closely connected with the idea of nonviolence toward animals (called "ahimsa" in India), and was promoted by religious groups and philosophers.
Following the Christianization of the Roman Empire in late antiquity (4th–6th centuries), vegetarianism nearly disappeared from Europe. Several orders of monks in medieval Europe restricted or
& 24th "tirthankaras" in Jainism respectively revived and advocated ahimsa and Jain vegetarianism in 8th to 6th century BC; the most comprehensive and strictest form of vegetarianism. Vegetarianism was also practiced in ancient Greece and the earliest reliable evidence for vegetarian theory and practice in Greece dates from the 6th century BC. The Orphics, a religious movement spreading in Greece at that time, also practiced and promoted vegetarianism. Greek teacher Pythagoras, who promoted the altruistic doctrine of metempsychosis, may have practiced vegetarianism, but is also recorded as eating meat