Dependent Origination
From SGI Quarterly

Buddhism teaches that all life is interrelated. Through the concept of "dependent origination," Buddhism holds that nothing exists in isolation, independent of other life. The Japanese term for dependent origination is engi, literally "arising in relation." In other words, all beings and phenomena exist or occur only because of their relationship with other beings or phenomena. Everything in the world comes into existence in response to causes and conditions. Nothing can exist in absolute independence of other things or arise of their own accord.
Shakyamuni used the image of two bundles of reeds leaning against each other to explain dependent origination. He described how the two bundles of reeds can remain standing as long as they lean against each other. In the same way, because this exists, that exists, and because that exists, this exists. If one of the two bundles is removed, then the other will fall. Similarly, without this existence, that cannot exist, and without that existence, this cannot exist.
At its essence, this interconnectedness transcends passivity and is dynamic, holistic and generated from within. More specifically, Buddhism teaches that our lives are constantly a synergy of the internal causes within our own life (our personality, experiences, outlook on life and so on) and the external conditions and relations around us. Each individual existence contributes to creating the environment which sustains all other existences. All things, mutually supportive and related, form a living cosmos, a single living whole.
When we realize the extent of the myriad interconnections which link us to all other life, we realize that our existence only becomes meaningful through interaction with, and in relation to, others. By engaging ourselves with others, our identity is developed, established and enhanced. We then understand that it is impossible to build our own happiness on the unhappiness of others. We also see that our constructive actions can positively affect the world around us. As Nichiren wrote, "That which you give to another will become your own sustenance; if you light a lamp for another, your own way will be lit." (Gosho Zenshu, p. 1598)
There is an intimate, mutual interconnection in the web of nature, in the relationship between humankind and its environment--and also between the individual and society, parents and children, and husband and wife.
If as individuals we can embrace the view that "because of that, this exists," or, in other words, "because of that person, I can develop," then we need never experience pointless conflicts in human relations. For instance, in the case of a young married couple, their present existence is deeply connected to their relationship--regardless of how positive or negative--with each other and with their respective in-laws. A person who realizes this interconnectedness can turn everything, both good and bad, into an impetus for personal growth.
Buddhism teaches that we "choose" the family and societal circumstances into which we are born to learn and grow and to be able to fulfill our unique role and respective mission in life.
On a deeper level, we are connected and related not just to those physically close to us, but to every living being. If we can realize this, feelings of loneliness and isolation, which cause so much suffering, begin to vanish, as we realize that we are part of a dynamic, mutually interconnected whole.
As Daisaku Ikeda has written, an understanding of the interconnectedness of all life can lead to a more peaceful world:
"The Buddhist principle of dependent origination reflects a cosmology in which all human and natural phenomena come into existence within a matrix of interrelatedness. Thus we are urged to respect the uniqueness of each existence which supports and nourishes all within the larger, living whole.
"What distinguishes the Buddhist view of interdependence is that it is based on a direct, intuitive apprehension of the cosmic life immanent in all phenomena. Therefore, Buddhism unequivocally rejects all forms of violence as an assault on the harmony that underlies and binds the web of being." (From "Peace and Human Security: A Buddhist Perspective for the Twenty-first Century" delivered on January 26, 1995 at the University of Hawaii)