Answer:
To combine his background in both ethnography and archeology to make a research study.
Explanation:
In his bid to study the experience of Mexican migrants attempting to cross U.S border, Joan De Leon used four field of anthropology to make the research
In his research work, titled The Land of Open Graves: Living and Dying on the Migrant Trail (University of California Press), which was published in 2015, he explained that, the reason for using four field of anthropology is to find the cultural background relationship, the linguistic aspects, the biological integration: forensic science, and as well the archeological endeavor that is involved.
In other words, Joan De Leon reason for using four field of anthropology for his research study, is to find, how undocumented migration is a global phenomenon, as it is not just a desert situation only, but stretches from North to South, involving all kinds of intellectual, methodical and political processes.