21,470 irregular migrants have died trying to cross the Mediterranean Sea between 2014 and 2020, and 7,261 irregular migrants have died while crossing the US-Mexico border between 1998 and 2017. Yet in Europe and the United States, irregular migration is framed as less of a humanitarian crisis endangering the lives of migrants and more as a security threat to the West, and consequently is met through the militarisation of borders. This paper utilises the literature on border militarisation and irregular migration on the southern borders of the US and EU to answer the research question: How does border militarisation affect irregular migration in the US and EU? The paper comes to the conclusion that the “prevention through deterrence” approach to irregular migration actively endangers migrants attempting the journey northward, while also failing to prevent irregular migration. Moreover, research conducted in the US shows that raising the migration costs through border militarisation decreases re-migration and therefore has effectively increased the population of irregular migrants in the US.