Will there ever be slavery again?

Answer 1

In the US, so long as our current government or something like it lasts, no. Slavery persisted in those times because agriculture was extremely labor-intensive, and since that time machines have been invented which do the tasks once performed by hand, mostly by slaves. The powers-that-be in the US do not need slavery, as the people have been disconnected from the land and thus also from the ability to feed themselves. Nowadays people must have jobs to live, and thus are "wage slaves", who must show up when and where told to, and do the assigned task no matter how disagreeable, and do it as instructed. So there is no need to own people whose own desperation keeps them doing what the big people need done. Moreover without slavery the bosses are not obliged to care for, house, clothe or feed the people. In recent decades there has been some window dressing applied to slightly ameliorate the harsher aspects of this modern way of life: Social Security, Medicare and Medicaid, public housing, unemployment insurance, food stamps, "welfare" in general, but only so much as is necessary to keep the people quiescent and not in a mood for revolution.

In other parts of the world slavery has never ended and flourishes to this day, in the Muslim world, parts of Africa, and Haiti, for instance.

[NEW RESPONDENT]

You're talking about official human rights under civilised regimes. But there is always the underworld, where slavery is rife, though not under that name. Wherever you have people-smugglers, drug-mules and crack-whores, you will have slaves, slave-owners and slave-drivers, no different from Uncle Tom's Cabin.