In some respects Hernandarias's tenure of office resembled that of Irala, for, although unanimously elected by the colonists, in whose eyes he was estimated at his true value, the official ratification of Spain of his appointment was many years in forthcoming, the principal reason for the delay being, of course, due to the fact of his colonial birth. On several occasions his government was interrupted owing to this, and, indeed, Hernandarias may be said to have ruled for various distinct periods. It was only on November 7, 1614, that he received the definite appointment as Governor from the Court of Spain.

It was at this period that the Government of the River Plate was separated from that of Paraguay, Buenos Aires being made the capital of the former, while Asuncion remained the capital of the latter. This process of subdivision was continued until, at the period when the Viceroyalty of Buenos Aires was constituted, it consisted of the provinces of Paraguay, Tucuman, Cuyo, the River Plate, Santa Cruz de la Sierra, and Charcas.

The value of these River Plate provinces was now become apparent to Spain. Lacking in minerals though they were, these south-eastern territories of the Continent were now exporting an amazing quantity of horns, hides, tallow, and other such produce of the pastoral industry. So abundant, indeed, had become the wild herds of cattle which roamed on the plains of the alluvial country that a stray buccaneer or two landed a force with the object of collecting horns and hides.

At a later period a French adventurer of the name of Moreau endeavoured to establish himself permanently on the Uruguayan shore for this purpose. He had already fortified himself, and had collected a considerable store of hides, when he was attacked by the Spaniards and driven from the spot. He returned to attempt the venture for the second time, but his force was again defeated, and on this occasion he lost his life.

The Indians in these provinces had now become expert horsemen. They, too, possessed their share of the enormous quantities of live stock with which the country abounded; but if from drought or any other such cause the numbers of their animals grew uncomfortably diminished, they would raid the European settlements, and, taking the colonists by surprise and slaughtering without mercy, would sweep the country-side clear of live stock, and scamper away to their own haunts at top speed.

Thus the hatred between the natives and the colonials grew ever more bitter, and weapons, ambushes, and massacres constituted the sole means of communication between the two. These Indians of the open plains proved themselves formidable enemies, and, utterly merciless as they showed themselves to the vanquished, they rapidly became a continual source of dread to the pioneers living in the remoter settlements.

In 1767, when the order was received from Spain to expel the Jesuits from the Spanish colonies in South America, the expulsion took place unattended by any untoward circumstances in such places as Córdoba, Corrientes, Montevideo, and Santa Fé. In these places the buildings that had been devoted to the objects of the Order were ransacked, and, unfortunately, many valuable collections of books and similar objects were destroyed.

The authorities regarded with more hesitation the carrying out of the orders from Spain in the province of Paraguay. Many tens of thousands of Indians formed part of the Jesuit settlements, and the influence of the Company was supreme throughout all the territories which now constitute North-West Uruguay, South-East Paraguay, and South-West Brazil.

Don Francisco de Paula Bucareli y Ursua, the Governor of Buenos Aires, marched north in order to effect the eviction. Bucareli's few companies of troops would, of course, in actual warfare have stood no chance whatever against the numerous Indian regiments which the Jesuit missions now possessed. Bucareli relied on his gifts of tact and diplomacy, of which he gave no small evidence during the negotiations which ensued. As it turned out, the employment of neither of these qualities, nor of the troops which he brought with him, proved necessary, for the Jesuits expressed themselves ready and willing to comply with the order, and, having obeyed it, they were escorted to Buenos Aires. From thence they were sent by ship to Europe, and the great social structure they had erected fell forthwith to the ground.

The districts which had formerly been occupied by the mission Indians became after a while practically depopulated, and the Portuguese, remarking this state of affairs, decided that the moment was favourable for aggression. Thus, in 1801, Portuguese troops from the town of San Pedro advanced against the Spanish port on the western shore of the Lake Patos, whilst others advanced towards the River Prado.