What are the main causes of slavery?

What are the main causes of slavery?
These seven factors led to the development of the slave trade:

The importance of the West Indian colonies.
The shortage of labour.
The failure to find alternative sources of labour.
The legal position.
Racial attitudes.
Religious factors.
Military factors.

These seven factors led to the development of the slave trade:
  • The importance of the West Indian colonies.
  • The shortage of labour.
  • The failure to find alternative sources of labour.
  • The legal position.
  • Racial attitudes.
  • Religious factors.
  • Military factors.