Bales finds two broad types of slavery. The "old" slavery (exemplified for many of us by the pre-Civil War United States south) was based on legal ownership and division along ethnic and racial lines. Slaves were expensive and relationships between slaves and slaveowners were often long-term, sometimes multi-generational. The "new" slavery, in contrast, is based not on formal ownership but on other legal instruments such as contracts and debts. Slaves are cheap, even disposable, and drawn from the poor, vulnerable, and dispossessed rather than from particular racial or ethnic groups.
These are of course ideal types and modern slavery mixes elements of both, varying in its forms both between regions and across individuals. Disposable People contains five case studies: sex slavery in Thailand; old-fashioned chattel slavery in Mauritania, with White Moor masters and Black slaves; charcoal-makers on the frontier in Brazil; brick-makers held in heritable debt-bondage in Pakistan, through fraud and dishonest accounting; and farmers in debt-bondage in India. In each case Bales presents the personal stories of a few individuals, analyses the economic and political causes of their slavery, and sketches its broader social and historical contexts.
Bales avoids sensationalism and takes care with his analysis. He distinguishes genuine slavery from mere poverty, arguing that "slavery should not be confused with anything else: it is not prison labor, it is not all forms of child labor, it is not just being very poor and having few choices". (Though the boundaries have to be a lot fuzzier than he lets on.) He also avoids moralising: slaveholders are not all cruel and in some cases slavery is deeply embedded in the culture — not all slaves yearn for freedom and some may be unwilling to repudiate debts or contracts, even when clearly fraudulent or unfair.
Common to all forms of slavery is the use of violence, overt or implicit. So slavery requires either a failure of the state to maintain law and order or its complicity. In each of his case studies Bales looks at the role of the legal system and law enforcement. Failure to protect slaves or enforce anti-slavery legislation may be the result of apathy, discrimination, or corruption; sometimes there is more direct involvement, with the police playing an active role in intimidating slaves and catching runaways.
Also common to all forms of slavery is a profit-making motive, though the profits from the "new" style of slavery tend to be much larger than from the older forms. Bales covers both microeconomic detail and connections with broader national and global economies. He analyses, for example, the profits to be made from owning a water-carrier slave in Nouakchott, Mauritania, or running a four-worker charcoal-making operation in Brazil. And he looks at the scale of the profits made by the businessmen with "clean hands" who run slave-using businesses "at arms length" and at their links to national and international companies and markets.
This economic connection is one of the ways in which Bales urges ordinary citizens in the developed world to act, by putting pressure on their pension and mutual funds. Another is political action, directed towards economic sanctions or to pressuring governments to enforce anti-slavery legislation. Disposable People also touches on the work done by international organisations such as Anti-Slavery International and local organisations such as the Pastoral Land Commission in Brazil, the mixed success of international campaigns against child labour in Brazil, the failure of a brick-makers "revolution" in Pakistan in 1988, and the relatively successful anti-slavery programs in India.
Ending slavery is no easy task: it is certainly more complex than simply making a proclamation or announcement (as the 1980 "abolition" of slavery in Mauritania demonstrates). Bales explains that "being free means more than just walking away from bondage"; to protect freed slaves from starvation or reenslavement, it is essential to provide education, training, and psychological support to enable them "to find their own way into true freedom".