The third crisis entailed a conflict with the Argentine Confederation regarding ascendancy over territories adjacent to the Río de la Plata and free navigation of that waterway. Since the 1830s, Argentine dictator Juan Manuel de Rosas had supported rebellions within Uruguay and Brazil. It was only in 1850 that Brazil was able to address the threat posed by Rosas. An alliance was forged between Brazil, Uruguay and disaffected Argentines, leading to the Platine War and the subsequent overthrow of the Argentine ruler in February 1852. Barman said that a "considerable portion of the credit must be ... assigned to the Emperor, whose cool head, tenacity of purpose, and sense of what was feasible proved indispensable."