The year 1816 was the blackest for the patriot cause since the beginning of the revolution. Chile had been reduced to obedience; the Argentine was convulsed by civil war; Uruguay had fallen into the hands of the Portuguese king; the Spaniards were triumphant in Venezuela, and New Granada, Ecuador, Peru, and Bolivia were making no resistance. Pezuela had been promoted to be viceroy at Lima and La Serna in the beginning of 1817 led the Spanish army into the Argentine and advanced far beyond the frontier. But he made his campaign according to the rules of regular European warfare, and though the gauchos of Salta did not venture to give him battle they kept up a harassing series of night attacks, ambushes, and daring forays into his very lines. Mounted on their fleet and hardy plains horses, living on wild cattle, and needing no baggage or provision train, their mobility was phenomenal, and they rendered the advance of the Spanish army through the long stretches of desert and pampa almost impossible. Meanwhile San Martin's great victory at Chacabuco in Chile completely changed the situation throughout the continent. It was necessary for the viceroy to drain the other provinces of troops to attempt Chile's recovery. Even if La Serna did succeed in pushing toward Buenos Aires, San Martin could recross the Andes and strike him in flank with a victorious army. So the Spanish general withdrew from the northern Argentine and took up the old position near the Bolivian border. The Argentines never attacked him in force, although they kept up a war with incursions over the frontier, and the indomitable Bolivian patriots rose in one local revolt after another during the next four years. The country was never pacified, although the relentless vigilance of the Spanish commanders prevented the insurrection from becoming general. In 1820 San Martin sailed from Valparaiso and landed his army of Argentines and Chileans on the Peruvian coast near Lima. His masterly dispositions soon compelled the Spaniards to evacuate the capital and thenceforth their power was confined to the Andean region which extends south-east from the Cerro de Pasco to the southern boundary of Bolivia. The patriots had the advantage of being able to land troops at any point on the coast, and the Spanish generals, to meet these invasions, were compelled to move their armies over the tortuous mountain paths. Late in 1822 an expedition attempted to reach the Bolivian plateau by the pass which leads directly up to La Paz. Valdez, the Spanish general, managed to get to the threatened point before the patriots had pushed their way up the mountain. They attacked at a disadvantage, and their army was destroyed.