In March of 1835 General Manuel Oribe was created the second constitutional President of the Republic. One of his first cares was to undermine the weighty influence of Rivera, in whose power he saw a menace to his own office. The new President began the campaign by summoning back to their country all those Lavallejistas who had been living in forced exile in Brazil and Argentina. Then, in order to deliver a death-blow to a rival's prestige, he deprived the late President of his rank of commandant-general.
Exasperated beyond endurance at this latter move, Rivera immediately made his appeal to the only authority that was understood at the period—that of arms. The insurrection attained almost immediately to formidable proportions. Indeed, there is no doubt that the malcontent cause would have been successful almost immediately had not Rosas intervened. As it was, the Dictator sent over from Argentina to the assistance of the Government five hundred troops, under the command of Lavalleja, who had thrown in his lot with Oribe against his arch-rival.
As a preliminary to the actual hostilities Oribe sent forth a thunderous proclamation, in which Rivera was branded as a traitor to his country. The first battle ended in favour of the Government, the forces of the rebellion leaving over two hundred dead upon the field. The chief historical importance of the contest, however, lies in the fact that on this occasion were used for the first time the red and the white colours that distinguished the respective forces of Rivera and Oribe and that have ever since remained the emblems of bitter strife.
The fortune of war varied for a while. After numerous indecisive skirmishes, Rivera won an action at Yucutuja, while a month later Oribe was successful in a battle on the banks of the River Yi. Then followed the decisive battle of Palmar, from which the Government forces emerged no longer as an army, but merely as a scattering of fugitive stragglers.
In the meanwhile foreign influence, in addition to the lot of war, had veered in favour of the revolution. The arbitrary methods of Rosas, extended to foreigners resident within the land, had caused him to become embroiled with France. Thus the northern power, in addition to the institution of a blockade of Buenos Aires port, was only too glad of the opportunity of frustrating the plans of the Argentine despot in Uruguay. Allying their forces with those of the revolutionists, they captured the island of Martin Garcia from the Government troops, and were preparing further active measures of aggression when Oribe realised the hopelessness of his plight. Adopting the sole course that was left him, he resigned his office of President, and sailed for Buenos Aires, accompanied by his late ministers, and a considerable following of private friends.
Rivera's road to the return of power was now clear. In November of 1838 he made a triumphal entry into Montevideo, and in due course the National Assembly elected him President for the second time. One of the first acts of the new chief of the State was the avenging of Rosas' late interference in favour of his rival. Allying himself with the French Government and the Province of Corrientes, he declared war—not against the worthy Argentine nation, as was carefully explained in the proclamation, but against the "tyrant of the immortal people of South America."
Rosas was never slow in responding to a challenge of the kind. Scarcely had the declaration of hostilities been made when he sent an army of six thousand men to invade Uruguay. Rivera, his forces strengthened by a thousand French volunteers, marched to meet the enemy, and at Cagancha he obtained a signal victory, the Argentine troops being defeated with heavy loss, and thus forced to abandon their campaign in Uruguay.
It seemed as though the event had put the seal upon Uruguay's success. But the fortunes of the period were as erratic as the period was turbulent. Very shortly after the Battle of Cagancha the differences between Rosas and the French were settled, with the result that an armistice was effected. With the raising of the blockade of Buenos Aires and the departure of the French troops from the country, it was the turn of Rosas to laugh, for his enemy now stood before him single-handed.
On this occasion the first aggressive steps were taken by the naval forces. In 1841 the Argentine fleet, under Admiral Brown, made a practical end to Uruguayan sea power. Some minor vessels that were subsequently collected were given in charge of the Italian Garibaldi, and the famous guerilla leader carried on with them a war of privateering, without, however, meeting with any material success.
In a desperate attempt to stem the formidable tide of Rosas's power, the three provinces of Corrientes, Entre Rios, and Santa Fé allied themselves with Uruguay. From the joint States Rivera raised an army of seven thousand men. But even this heroic effort did not suffice. Boldly marching through Entre Rios towards Buenos Aires, Rivera found himself brought to an abrupt halt by the unexpected appearance before him of his old enemy, Oribe, at the head of an imposing army of fourteen thousand men. The ensuing battle, fiercely fought, ended in an overwhelming victory for the superior forces, nearly a thousand of Rivera's men being massacred in cold blood on the conclusion of the fight.