Buddhism is a religion or traditional way of life which was founded by Shakyamuni (Gautama) Buddha in Southeast Asia, specifically the Gangetic plain, around 500-400 BC. The Buddha was born a prince of the Shakya clan in the town of Lumbini, in what is now Nepal. Around his coming of age as a young man, Buddha renounced his royalty and left to become a wanderer. During his journeys, which are documented in traditional texts, Siddartha Gautama sat under the Bodhi tree at Bohd Gaya in Bihar, India and attained enlightenment. Buddha is thus a title given to those who have become enlightened. Buddhists comprise more than 500 million people worldwide across East Asia, MENA, and, more recently, in the Americas and Europe.
Buddhism is a form of Stoicism philosophically. It teaches that suffering (Dukkha), or dissatisfaction, is a condition inherent to human existence. Buddhism seeks enlightenment which allows one to be unattached. This lack of attachment liberates the Buddhist from unnecessary suffering, whether it be physical, psychological, spiritual, or emotional in form-- there is no attachment held for their current life, the family, friends, associates, or strangers who accompany them in this life, their physical pain or illness, the concrete world and its laws, or its emotions regarding any of these forms of attachment. Buddhists see this attachment as the barrier to enlightenment because they believe that the realizations that all being is in eternal flux, that all things are interconnected and coincidental, that all existence is fleeting no matter the scale-- this liberates the sufferer to be able to act as a pragmatic subject which has no wants and few needs. Historically, however, Buddhism's inability to fully address the contradictions between its worldview and collective human being prevented it from developing as far as Taoism or Confucianism.
Buddhists believe that humans are reborn after death, and that they are reborn into good or bad realms depending on their intentional actions, or karma. Such actions are supposed to be honed during a particular lifetime in order to achieve merit in the next life. This cycle of suffering, in which the very act of existing is mediated by struggle and desire, is called samsara. This cycle of death and rebirth, of suffering and the end of suffering, can only be stopped when one becomes enlightened and ceases craving.
The traditional worldview and spiritual beliefs of Buddhism communicate various aspects of the dialectical tradition of thought; namely, the interconnectedness of being, the contradiction/tension within all things, the importance of having a sobering pragmatic outlook, the necessity of objectivity and detachment, and alienation, among others. This is why many nations with Buddhist majority or large minority populations are Communist or socialist, or have prominent Communist parties involved in their political affairs, including China, Mongolia, North Korea, Vietnam, Cambodia, Laos, Sri Lanka, India, Russia, Thailand, Nepal, and more.