The question of trafficking in human beings is not new to international law. Already during the late 1800s, several countries in Europe became concerned with the prostitution, movement and procuring of European women and children abroad. This concern resulted in an international conference in Paris in 1902 on the issue of the white slave traffic. As a result of the conference the "International Agreement for the Suppression of the White Slave Traffic" was agreed upon, focusing on preventing the movement of white women and girls, in particular, for immoral purposes abroad. This was followed by a Convention on the same issue in 1910 ("the International Convention for the Suppression of the White Slave Trade"). Allain (2017, 30) argues that these two treaties and the negotiations that preceded them show at least three things: 1) how European countries at the turn of the century in their diplomatic relations started moving from bilateralism to multilateralism, i.e. a shift from diplomatic liaison and negotiations between two countries to negotiations involving several countries; 2) that the participating countries agreed, perhaps for the first time, that the idea of such negotiations was to produce international law that would not only apply internationally, but would be ratified also nationally, i.e. be incorporated into domestic legislation, and; 3) that although countries came to the negotiations with different aims and ideas concerning the regulation of prostitution and the movement of women, they managed to find common ground, i.e. compromise in the issue of criminalising the exploitation of the prostitution of adult women, and criminalizing all prostitution of minors.

These early treaties also brought the issue of trafficking – then called traffic – to the international agenda as an international concern. It is today evident that these concerns were racist and protectionist (since the focus was largely on European, white women only), but elements of the early definition of "traffic" were to be incorporated into the international negotiations concerning the definition of "trafficking in persons" almost 100 years later.

See Allain (2017) for a thorough discussion on the "white slave traffic" and the relevance of the early international treaties.

See Morcom and Schloenhard (2011) for a detailed outline of the evolution of international law on trafficking:
Morcom and Schloenhard (2011) argue that the current understanding of trafficking in persons has in fact been influenced by five different areas of international law, namely: 1) slavery, 2) prostitution, 3) labour (including issues relating to migrant labour), 4) human rights, and 5) the rights of the child. They also argue that international law has addressed trafficking in persons, largely from a criminal justice (or law and order) perspective, and that the current conceptualisation of trafficking combines very different branches of international law, leading to a definition which is at times difficult to interpret and apply.