In the modern economies, mechanization generally made forced labor economically inefficient.
Although this may become true as automation becomes able to do more things more cheaply, China seems to be a very strong counterexample at our current/recent technological level. Prison slaves, Forced student labour is central to the Chinese economic miracle, Laogai or "reform through labor" programmes, etc. America's prison labor system is also quite scary.
I'm curious as to why this was downvoted? China is definitely at the industrial level and there appears to be strong evidence for forced labor driving parts of the economy, which seems a relevant counter to the suggestion that there's not an economic incentive to enslave groups in the industrialized world.
Perhaps extracting forced labor from an internal group rather than captured neighbors is a more important distinction to some people?
Historically, the evolution of government systems was mainly driven by violence, with invasions and revolutions being the principal agents of selection process. The rules of the game were predetermined by our environment - land was a limited resource, for which our ancestors had to compete, if only to ensure the survival of their descendants.
The 20th century introduced a game changer. As agricultural productivity in developed countries rose by orders of magnitude and natural population growth practically came to a halt, possessing a large territory stopped being a necessity. Countries with little arable land, ultra-high population density and no natural resources can now not only feed their population, but also achieve top living standards. These changes may open a fundamentally different route for societal evolution – one that would not be based on violence or compulsion.
A small thought experiment - imagine what would happen if central governments cede most powers to smaller territorial units:
Unfortunately, there are serious obstacles to the successful implementation of this idea:
Do you think these problems are solvable?