The Australia-based Walk Free Foundation has compiled an index ranking 162 countries by their prevalence of modern slavery. The following countries top the list, by prevalence of population.

1. Mauritania: Primarily "chattel slavery" in which adults and children are considered "full property of masters."

2. Haiti: High poverty contributes to "restavek" - poor children sent to work for wealthier families.

3. Pakistan: Weak economy, deteriorating security and growing population contribute to an increase in enslaved children and bonded laborers.

4. India: Problems include inter-generational bonded labor, child labor, sexual exploitation and forced marriages.

5. Nepal: Primarily forced labor and forced sex work. Country is transit point and destination for modern slavery.