What factors led to the xenophobic attacks happening in South Africa?

The past few days haven't been very interesting in South Africa, especially if you are a foreigner. A wave of attacks were carried out against black foreigners in South Africa and their businesses.

Many lives have been lost with people being burned or macheted in the streets. Countries like Zimbabwe is taking their citizens back home. Some other African countries are also doing the same.

The question is, what do you think are the factors that led to the xenophobic attacks against foreigners in this country that used to represent freedom for AFrica?