I have always felt that the contemporary struggle to end poverty is one of the most important challenges facing humanity. But as we approach 2015, the target year of the millennium development goals (MDGs), it seems the struggle is failing because we are forgetting where it must be fought.

The International Labour Organisation estimates there are around 21 million people in slavery across the world today. And yet the struggle to end, finally, this most abject form of exploitation remains of marginal concern in the development community.

Senior NGO staff in the UK and elsewhere in Europe have told me that the reduction in poverty they are working to achieve will erode the causes of slavery. But the causes are fundamentally about the political and cultural mechanisms of excluding people from economic and social justice. Unless development projects and campaigns consciously seek to undermine that exclusion, they will fail to remove people from slavery – and consequently from poverty.

Slavery in the modern world varies from trafficking for sexual exploitation, to forced labour of children as domestic workers, to forced labour of girls in manufacturing garments for high-street brands in Europe.

However, research by Anti-Slavery International and others shows that while slavery takes many different forms there are, at core, three important commonalities. First, those who are subject to forced labour tend to be vulnerable individuals, usually economically but often socially. Second, they come from communities that are socially excluded and discriminated against either in their home country, abroad, or both. Third, the governments of the countries in which they are abused – by design, a lack of capacity or corruption – fail to ensure proper standards of social and economic justice and the rule of law.

Put another way: slavery occurs to those deliberately or unthinkingly excluded from social and economic development, justice and rule of law. That is a human rights issue and also a political one. Any development project that does not recognise this threatens to overlook some of the intractable problems of poverty that continue to plague the world.

The failure to recognise the centrality of human rights in the struggle against poverty is exemplified by the MDGs: there is no mention of slavery or child labour in these goals; neither is there any mention of the importance of reducing non-gender forms of discrimination and prejudice. And although there is an MDG to promote gender equality and empower women, there is scant reference in relation to this MDG of the imperative of reducing violence against women and girls – something that is often associated with contemporary slavery.

For too long development programmes have been blind to the power dynamics that underpin slavery. As they stand, the MDGs could conceivably be achieved without affecting the life of a single person in forced labour. In fact, their lives could be worsened as they are left behind in the development project.

However, affirmative action programmes of social and economic justice that focus on the vulnerability of individuals within socially excluded communities would stand a good chance of breaking the cycles of slavery and other rights abuses.

For example, ensuring universal access to quality education for dalit girls in south Asia would be just such a programme, particularly if undertaken in a context where states are making concerted efforts to eliminate discrimination and ensure acceptable standards of rule of law for all.

Of course, ending slavery doesn't depend solely on development agencies and aid projects focusing on the issue. It requires safe migration for poor people seeking work to find better lives for themselves and their families. It means the trade union movement seeking innovative means of organising workers to protect those who are vulnerable or underage, in the formal and informal economies. It means holding to account transnational businesses that deliberately or thoughtlessly contribute to the exploitation or enslavement of workers. It means extending the rule of law nationally so that all citizens have access to legal remedy and redress, properly administered.

The steps needed to end slavery can be taken, given concerted political action. Martin Luther King said: "The arc of the moral universe is long but it bends toward justice." He was right, because human beings act to twist it in that direction. Unfortunately, without proper understanding of the importance of human rights in the struggle to end poverty, efforts to bend that arc in the direction of justice will remain askew.