Montevideo seemed doomed to an early surrender when an opportune intervention by France and England upset the plans of Rosas. He had embroiled himself with the ministers of those powers by refusing to give satisfaction for certain alleged injuries to foreign merchants and naval officers, and the dispute became so acrimonious that the European powers finally resorted to the most drastic coercive measures. A French, and later a British, fleet blockaded Buenos Aires and drove Rosas's vessels from the Plate. Under these circumstances it was impossible for him to land re-enforcements on the Uruguayan shore. In 1845 the European navies forced a passage at the head of the estuary into the Parana and Uruguay, destroying the batteries which Rosas had erected there and opening up those rivers to foreign navigation. Thereafter, troops could be sent from Argentina into Uruguay only by a long detour to the north. In spite of this hampering of his military operations, and the injury which the blockade caused to the commerce of Buenos Aires, the Argentine dictator stubbornly refused to yield an inch to foreign pressure. France and England were finally tired out; they raised the blockade; Rosas regained his control of the Plate and the early capture of Montevideo seemed certain. Just at this time, however, General Urquiza, governor of Entre Rios, and Rosas's best lieutenant and most successful general, broke with his chief. Entre Rios became a virtually independent state, and Rosas's efforts to reduce it were unavailing. Urquiza's defection again rendered it impossible properly to reinforce Oribe's army. The colorados of the interior plucked up courage and during four years no material progress was made on either side. A tedious and exhausting partisan warfare went on in the interior; guerrilla bands scoured the country in every direction; inhabitants of the same town were arrayed against each other, and surprises, treasons, and massacres were almost daily occurrences. One of the most successful leaders on the colorado side was the famous Giuseppe Garibaldi. The future liberator of Italy had made his debut as a revolutionist in the insurrection which broke out in 1835 in the Brazilian province of Rio Grande. Later he crossed the Uruguayan border and fought against Rosas for several years.