Since Sudan’s Comprehensive Peace Agreement (CPA) was signed, its border with Uganda has become a hub of activity. Contrasting developments on the Ugandan side of the border with those on the South Sudanese side, the paper draws on empirical fieldwork to argue that the CPA has created new centres of power in the margins of both states. However, in day-to-day dealings on either side of the border, South Sudanese military actors have become dominant. In the particular case of Arua and the South Sudan–Uganda border, past wartime authority structures determine access to opportunities in a tightly regulated, inconclusive peace. This means that small-scale Ugandan traders – although vital to South Sudan – have become more vulnerable to South Sudan’s assertions of state authority. The experience of Ugandan traders calls into question the broad consensus that trade across the border is always beneficial for peace-building. The paper concludes that trade is not unconditionally helpful to the establishment of a peaceful environment for everyone.