After Oribe's accession to power Rivera hastened to raise a revolt in the western districts. He obtained help from the unitarians, and his invasion was accompanied by many Argentine generals who had distinguished themselves in the wars against Rosas. The Argentine dictator sent help to Oribe, but for two years the tide of battle set in favour of the colorados and unitarians. Rivera had obtained so decided an advantage by 1838 that Oribe abandoned Montevideo and embarked for Buenos Aires, followed by the chiefs of his party. The colorado chief, now in control of all Uruguay, celebrated a formal alliance with the province of Corrientes, then in revolt against Rosas, and war was declared against the latter. A large Argentine army, accompanied by many blancos, invaded Uruguay, but was decisively defeated at the battle of Cagancha, December 10, 1839. The interval of unquestioned colorado supremacy which followed was one of the most flourishing periods in the history of Uruguay. Large numbers of the intellectual elite of Buenos Aires swarmed across the river; Montevideo became the centre of arts and letters of Spanish America; the civil wars of the last few years had not been severe, and even during their continuance property had suffered little. Immigration from England, France, and Italy began on a large scale, and the population increased at the rate of four per cent. per annum. In the year 1840 nine hundred ocean-going ships entered the port of Montevideo, more than three thousand houses were erected, and twenty-seven great meat-curing establishments were in active operation. However, Rosas and the blancos were only awaiting a good opportunity to attack. In 1841 Oribe, in command of one of Rosas's armies, defeated the Argentine unitarians under General Lavalle, and marched into Entre Rios to suppress the insurrection in that province. In January, 1842, Rivera took an army of three thousand men to the rescue of his unitarian allies. He crossed the river Uruguay and united his forces to those of General Paz, but after a year's desperate fighting on Argentine soil he and the unitarian general were overthrown and their armies completely destroyed in the battle of Arroya Grande. The way was open to Montevideo; the colorados and Argentine exiles shut themselves up in that city, and the so-called nine-years' siege began. Rosas's power seemed overwhelming, and although Rivera and other colorado chiefs at the head of scattered bands managed to make some headway in the outlying departments, they were finally driven into Brazil, while the unhappy country was given up to pillage and slaughter. This _guerra grande_ was the bloodiest, longest, and most stubborn war ever fought on Uruguayan soil.