Buddhism divides incarnations into realms. They are referred to as the "Six Styles of Imprisonment", and Buddhists believe we all, sooner or later experience each of them. A hell realm, a hungry ghost realm, an animal realm, the human realm, the jealous god realm, and the god realm.
So for Buddhists there are potentially billions of gods too, indeed the Judeo/Christian/Muslim/Hindu ones could all be included there. It is often asked of those who believe in reincarnation, "Taking into account population growth, where all the 'new people' are coming from?" This is where they're coming from according to Buddhist belief.
The Hell Realm
The hell realm is the lowest of the six realms, and an incarnation here is caused by extreme aggression. There are actually two kinds of hell in the Buddhist lexicon, one burning hot and one freezing cold. One is the result of the heat of rage, the other the product of icy hatred. In the hot hell, beings attack and kill each other over and over. Beings here are ceaselessly tortured by servants of Yama, the Lord of Death. But these torturers are not external creatures as Christianity defines devils, They are projections of the minds of the residents trapped in the realm. The only sentient beings in this realm are those who suffer there, and they are only trapped there by their own aggression and rage. In the cold hells people filled with pride and hate, bitter resentment and self-loathing, encounter self-enclosed isolation. No external tormentors here. Surrounded by walls of ice, their own reflections torment them. Some forms of Buddhism also speak of ephemeral hells which last for a much shorter time. beings can be trapped in ordinary inanimate objects such as rocks, lakes, or trees. These sufferings are usually considered the result of single actions or actions done within a single lifetime. In the other hells, life lasts for hundreds of thousands of years relative to human time. This is because for a person in such misery, time seems to hardly move at all. Liberation from this realm comes when a hell being begins to feel remorse or pity for another inhabitant. The barest glimmer of compassion is usually enough to result in a rebirth in a higher realm.
It should be noted too, that even in this bleak realm, the Buddha and the path of liberation exists. Yama, the Lord of Death is also described as the Dharma King, Dharmaraja. According to Indian legend, he was the first mortal to die, so he became a guide to others. Even in the Hell realm, though comparatively unlikely due to the fury of the realm, enlightenment and COMPLETE liberation is possible here. Just as with any other realm, if the sentient beings there can let go of their illusions, they can liberate themselves.
The Hungry Ghost Realm
The hungry ghost realm results from a life where extreme frustration and unsatisfied desire ruled your consciousness. In a life previous to this form of existence a being acted with extreme avarice, greed, meanness, or stinginess. It has nothing to do with external conditions. Even a billionaire can have the mentality of a hungry ghost. The suffering is less intense here. They don't feel as oppressed or confined, but the suffering is still significant due to the weight of the negative actions that have caused them to be born in this state. In this realm, beings wander endlessly, obsessed with what they lack. They live as wraiths, in desolate places. Some have died violent deaths, and are still bewildered by pain and fear, some are malevolent or twisted in some way, some are there because they want to injure others because of injuries which have been done to them in the past. Again, they have no real, inherent lack of abundance in this realm. Everything they need and want IS THERE, but their delusion prevents them from seeing it, and if they see it, their insatiable hunger prevents them from enjoying it. They are so totally obsessed with satisfying their own needs, that they cannot afford to feel the pain of others. The Buddha in this realm is called Jvalamukha, the Mouth of the Flame. He glows with limitless light and warmth which can never be drained away. He holds a vessel of ambrosia to satisfy every need. To liberate oneself here, one would have to give, or engage in hope, being willing to accept gifts and pass them on.
The Animal Realm
The animal realm is one in which there is only consciousness of the self. Of immediate needs. Hunger, sex, rest. All activity is directed towards satisfaction of immediate needs and desires. All is instinct, no reflection. They have ranges of perception that humans do not, but reasoning and intellect are underdeveloped. They perceive the world entirely in relation to themselves, with no deeper meaning. Animals are far deeper in the delusion of self and object duality. The suffering here results from the struggle for survival. Killing or being killed. And most often by us in the human realm. Trapped, manipulated, and controlled by us. The voluntarily ignorant, those
obsessed with hierarchy, those distrustful of outsiders, who are intolerant, or blindly led, those who have intellect but lack the imagination to use it, all may end up in the animal realm. Basically existence here is the result of mindless ignorance. In this realm, the Buddha appears as Dhruvasimha, the Steadfast Lion. He holds a sacred text in his hands, as a Buddhist symbol the text itself represents the dharma (teaching) itself. This is significant because language marks a crucial stage in the evolution of consciousness. The ability to reason beyond duality of subject and object. It is this higher intelligence which must be awakened for those in the animal realm to be liberated. By seeing the book, they are offered a glimpse of a different world and within the gap of uncertainty, enlightenment is possible. Am I asleep? Am I awake? Is this real life, or delusion? The act of questioning itself offers liberation.
The Human Realm
The human realm (though to be fair to other intelligent life, this is more accurately described as a middle realm not excessively burdened by negative past actions or deluded with power as in the god realms) is the one most likely to lead to ultimate liberation and enlightenment, so comes with much merit. Existence as an intelligent sentient being like this should be viewed as a magnificent opportunity. You've gone through the ringer to get here, don't blow it. The Buddha of this realm is Shakyamuni himself. Liberation here comes from renouncing pride, hate, status, things, desire, and attachment. To plunge the mind into the open space of wakefulness to see the unity of all. The searching energy of intellect makes it possible to open up to new possibilities and be receptive to spiritual teachings. Humans walk the razor's edge between the delusions of other realms. All the challenges of other realms, greed, power, hate, ignorance, desire, pride, meanness, arrogance, delusion -- all exist here and can be defeated here. That is why it represents such a huge challenge and opportunity.
The Jealous God Realm
The realm of demi-gods, also referred to as jealous gods, are beings are continually at war with the beings in the god realm, provoked and driven by jealously and envy of those in the god realm. In sanskrit they are called asura, which literally translated means "anti-god". Still, in this realm positive karma outweighs negative karma. They are actually seen as the elders to their brothers and sisters in the god realm. Fundamentally they have the same divine nature, intelligence and powers. But this is not viewed as auspicious as a human birth, because despite their intellect, power, and potential, they can easily fall into the three lower realms of hell, hungry ghost, or animal. Their tendency towards aggression and violence often makes them appear demonic. Their delusion lies in their jealousy of others which often leads to aggression (hell realm rebirth), their need to take sides (animal realm rebirth), and a desire to have status (hungry ghost realm rebirth). They are capable of doing great good as well as great evil, and possess a tremendous energy. If they are attracted to religion it is to acquire power. One becomes a jealous god after becoming discontented with the god realm. Essentially once the positive karma that caused a birth as a god is exhausted, the only way to go is down. The god realm is a land of perfection, of total pleasure and order, and the jealous god realm is a rebellion against that. The desire to express one's energy without contsraints of order. Once you experience discontent it is no longer possible to relax and enjoy the blissful existence of the gods. Yet you envy those who still can enjoy it, you feel cheated for losing what by rights should be yours, and feel shut out and excluded. Suddenly no one can be trusted. In addition to envy, paranoia is a delusion of the jealous, demigod realm. The Buddha in this realm appears as Vemachitra who tells of Buddha's message of compassion and abundance but the jealous gods cannot hear him because they distrust his motives. Vemachitra appears as invincibly peaceful and absolutely powerful and so just blocks all their attacks until they are forced to confront themselves. Here they must release their paranoia, and envy to find liberation.
The God Realm
However some of the jealous god's paranoia may be justified, for one thing the god realm possesses that the jealous god realm does not, is the elixir of life. According to legend, jealous gods don't possess it, because the god realm tricked them out of it, and now taunts them with it. The god realm is a realm of indulgence. In Buddhism there are three heavens. One of desire, one of form, and one of formlessness. The first is the world of the senses, including the pleasures of the mind. All the other realms of existence are within this heaven. They can see all but experience no pain. They are free from attacks, and experience bliss. Humans can be reborn in this heaven by following conventional religious practices and doing good deeds. They are still within the world of desire, but this is considered to be a fortunate rebirth, the result of many lives of virtue. The difficulty here is that there is so much pleasure and fulfillment, that one has little motivation to practice the dharma, so advancement PAST this point is extremely difficult. Mara, the Lord of Death, the one who tempted the Buddha on the eve of his enlightenment rules in this heaven. He represents the seductive aspect of spirituality, and feeds the ego that we are making great progress and becoming highly evolved beings. The heaven of form does not mean materialism, but simply the qualities of appearance, color and shape. Beings in this world have lost their attachments to coarse sense perceptions. They experience themselves as immaterial and are said to have subtle bodies of light. In the formless heaven, beings have transcended even appearance. They have abandoned all senses except the mind and have no visible form. Since these beings have no physical bodies they do not undergo death as we conventionally define it. They have immensely long lives, and then simply wake up in a different realm. In each of these heavens there are 21 levels of profound meditative states, each represent increasing purification. Above these are five levels known as pure bodies, the highest of which Akanishtha, is where the Buddha became enlightened. He moved his consciousness into this realm via disciplined meditation, despite "existing" in the human realm. In other words, through meditation he transcended all realm, all form, all formlessness. He just flat out went BEYOND. It is extremely difficult to attain enlightenment because you have trouble distinguishing subtle grasping from genuine realization. It's quite the hat-trick. If any attachment remains, you confront ego and only experience this state as a union with God or a Formless Absolute, for as long as there is a Self to attain union, there must also be a transcendent other with which to be united. When a being in the god realm experiences this it often results in grasping as a means of self-preservation, and so delusion remains. At the peak of this there is extreme doubt and the being isn't certain whether they are becoming enlightened or actually going insane. At that moment of ambiguity the being can either leap into the awakened state, or fall back into godlike trance. In this realm, the Buddha appears as Shatakratu, Performer of a Hundred Sacrifices. He plays a stringed instrument and speaks to the gods in the language of music because it is the one they are most likely to listen to. The moments of silence are just as essential as the moments of sound. Music is constantly changing, movement is it's very existence - it is the perfect teaching on impermanence for the gods, who are so attached to immortality and eternity.
