The recent political and economic crisis in Venezuela has fuelled an exodus of people in search of refuge and opportunity. By 2021, there were an estimated 6 million Venezuelans who had left the country as a result. The majority have travelled to countries within Latin America and the Caribbean, sparking a regional response involving international humanitarian support. While many travel to Spanish-speaking countries, including Colombia and Peru, a number of people journey by land across the shared border with Brazil. Many enter the country as temporary migrants, although Brazil's adoption of the Cartagena Declaration (exclusive to several Latin American states) has meant that many also gain recognition as refugees. In response to the increase in Venezuelan arrivals and the vulnerabilities that many experience, Brazil's federal government launched a humanitarian task force in 2018. This structure is comprised of several state agencies, international organisations and national civil society groups. Together, these entities perform under the banner of the 'Operacão Acolhida' or 'Operation Welcome' task force. Situated in the relatively isolated northern state of Roraima, bordering Venezuela, this research explores the response to Venezuelan migration. While many government agencies are involved, the military plays a particularly important role on the ground. Working alongside humanitarian actors, military personnel deliver aid supplies, construct and manage shelters, as well as enhance security at the border. This collaboration between the state, the military and the humanitarian realm raises questions about the logic underpinning the response and the implications this has on the lives of Venezuelan migrants and refugees. Upon investigation, a logic emerges that reveals a tension between the ways in which vulnerable mobile groups are offered support, while at the same time, they are tightly governed for the protection of state security. This thesis explores this logic by considering the legacies of militarism and violence within Brazil's distinct postcolonial context. Nestled under the umbrella of social and cultural geography, this research engages feminist political geography as a frame to connect scholarship from critical humanitarianism, mobilities, and Jasbir Puar's (2017) seminal work on debility. Drawing on a range of methodological approaches, including volunteer-research with humanitarian organisations and spatial ethnography, this research investigates the myriad infrastructures, actors and environments that work to govern migrant mobility. I visited the state of Roraima in November 2019, where I stayed for two months volunteering with a humanitarian group focused on supporting urban Venezuelan migrants living without adequate shelter. During this time, I conducted several indepth semi-structured interviews with key actors, engaged in multiple informal conversations, and made ethnographic observations across urban sites and formal spaces of care. By triangulating data and pulling together literature across various fields, I offer a different pathway for thinking about mobility governance in Brazil. I argue that the management of migrant mobility is founded on the logic of debilitating mobilities, which emerge through subtle forms of violence. This logic permeates Brazil's military-humanitarian intervention and manifests through multiple practices, infrastructures, spatialities and temporalities. Consequently, debilitating mobilities reinforces migrant vulnerabilities, keeping them in a cyclical loop of exclusion. This mobility governance and the subsequent implications occur across a range of geographical scales, including cross-border, urban and the intimate scales of the body and the personal. Rather than attending to the militarised security efforts of the Global North against mobilities streaming from the Global South, this research contributes to knowledge by addressing South-South mobilities and emergency governance. This approach provides an insight into the different, and equally significant geographies of Brazil and Latin America more broadly.