As the number of refugees continues to rise globally, so do concerns about responses from host communities. This project examines how the presence of refugees affects national identity formation and political participation for nearby citizens, particularly in understudied developing contexts where state capacity and national attachments are considered low. I theorize that exposure to refugees leads host citizens to more strongly identify with their national identity as a way to distance themselves from a new migrant out-group. Coupled with feelings of relative deprivation with respect to humanitarian aid, this heightened solidarity with co-nationals drives citizen participation in demanding better public goods provision. I test this theory in a border region of Tanzania that has hosted an influx of over 230,000 Burundian refugees since 2015. Drawing on experimental survey and community focus group data of over 2,000 citizens, I find that greater exposure to refugees substantially increases national identification, resource resentment, and participation in public goods. Additional analyses using geo-referenced primary school outcomes and interviews with government and NGO officials suggest positive downstream effects on public goods outcomes. By showing that animosity towards outsiders has consequences for national identity formation and development, this project highlights alternative pathways to nation-building.