Modern versions of slavery and people smuggling are closely connected.   Very often people who think they are headed for a chance to earn a living find themselves in situations that are in effect a kind of slavery, where they may be without pay or any escape, and subject to violence.

The distinction between some kinds of indentured work and slavery is very dubious - it's worth remembering that when rationalising and legitimising the institution of slavery in the United States the courts avoided using the word slavery or slaves, and used terminology about bonded labour and so forth.