The beginnings of Zen can be traced to India in the 3rd century when we have a school called Buddha Nature, which claimed that Buddha's emptiness is a gift we all share. That Buddha's nature is a connecting force between all that exists. 

The practice found a lot of traction in China through monks like Bodhidharma. The reason is that the interconnectedness the Buddhists were talking about matches the Tao, the connective substance, which is the basis of Taoism (one of the main Chinese schools of thought alongside Confucianism). From China, it moves to Japan, where the Zen name comes from.

Zen builds upon core Buddhist philosophy. One reaches Zen in 2 ways:

• through principle: understanding that we are all of Buddha-nature, underneath the world ignorance. The problem is conceptual: our ideas and thoughts are mediated by ignorance. 
• through practice: without practicing. Because once you get involved in the practice you elevate the ego.

Zen is really suspicious of concepts, words, etc. To get to the bottom of it one has to eliminate all words. To clear the mirror of our minds and let the dormant Buddha-nature shine.