The perquisites for being a witch are not fully understood. Only women can become witches and thus wield magic; the kinds of women who become witches tend to be social outcasts, women who feel society has failed them and, either by choice or obligation, alienate themselves from it. There are two paths to witchhood.
The most common is to be approached by Mature Nature - disguised as an elderly woman - and be offered a chance to forge the contract. Mother Nature knows when and where to appear, the women she selects are desperate - none have the heart to turn down the contract. Or maybe some do, but none ever hears from them again.
The second way is to summon Mother Nature. Although the consensus is that none would voluntarily become a witch, there are those who desire Mother Nature's power above all else. Summoning Mother Nature is a gruesome business the details of which are kept secret. Witches who voluntarily choose to become so are frequently fuelled by rage, hatred and vengeance; it shows in their magic, which is exclusively destructive.
Aside from the persecution, the life of a witch is made miserable by the knowledge that any second, she could explode. When discussing witches, the term explode refers to the utter loss of control witches display shortly before their end. When this happens, it is civilians who pay with their lives - and it is for that reason that witches are seen as a danger. Nobody knows why explosions happen or if there are any ways to prevent them.
Due to the world's hostility, witches frequently band together for safety. Nowadays these groups hardly reach half a dozen members, a stark contrast to the covens with hundreds of members that used to exist in the past. Groups of witches do not welcome new members, sometimes aggressively so.