The behaviour of regional powers towards their own regions is often volatile in the developing world, which leads to unstable integration processes. This article argues that this volatility is due to limited intra‐regional gains from regional integration in developing regions, which implies that the behaviour of regional powers is constrained by extra‐regional economic interests. When regional integration is not in conflict with extra‐regional interests, regional powers provide regional leadership. However, when extra‐regional interests are in conflict with regional integration, regional powers become regional Rambos. This argument is illustrated with the two examples of Brazil's behaviour in Mercosur and South Africa's behaviour in SADC. Both regional powers provided leadership during some periods of the regional integration processes, but became Rambos when important extra‐regional interests were at stake. This damaged regional integration processes in South America and Southern Africa considerably.