As the oldest surviving tradition of the world we have gone through many things over the millennia. Much misunderstanding exists about what Hindu Dharma is and is not. These misconceptions are a result of both outside influences and inside neglect.
There are many religions in this world with followers; most religions are Historic, meaning a person at a given point started each of these religions. The वैदिक सनातन Hindu Dharma(हिन्दू धर्म) is unique, as there is no beginning, no person started it! How can that be? A fact nearly impossible to understand for those who rely on history for their beginnings and whose perspective of time is linear as opposed to cyclical.
The best way to understand is by another question, who began Physics? A person may have discovered it at a particular time but physics was always there. In fact, baby monkeys knew the law of Gravitation before Sir Isaac Newton, otherwise they would not hold on to their mothers so tightly! True?
So the वैदिक सनातन Hindu Dharma,(हिन्दू धर्म) which is based in a concept of Dharma,(धर्म) is like that. Each of the words in the name I used is important. First, Vedic,(वैदिक) as it originates from the ancient most surviving literature of the world called the Vedas. वै सनातन, because it is like a physical law that exists at all times. When there is a manifestation like our Creation, certain laws exist and continue to exist as long as the creation lasts, hence सनातन (ever existing). Then the name Hindu, given to us by people who did not have the sound of SSSS in their language or found it difficult to pronounce, so instead of Sindhu or people of the Sindhu River they called us Hindu. However, Sanskrit(संस्कृत) being a well-done language (that is what it means sam = well kritam = done) has been given a beautiful meaning by my Guru:
हिम अपशब्दम दुष्यति खण्डयति इति हिन्दू:
Him apashabdam dushyati khandyati iti Hindu
This is derived etymologically and means: that Hinam word is bad; one who destroys अधर्म or unrighteousness is a Hindu.
I tell you this to clarify our stand on अहिंसा. To protect the धार्मिक and rid the world of अधर्म is a duty. So अहिंसा परमो धर्म is only, in reference to being the aggressor. Always, among Hindus defense was looked at as essential to preserving society. In the Bh. Geetaa Lord Krishna(गीता लार्ड कृष्णा) has made it clear again and again.