Urquiza was elected the first President under the new constitution for a period of six years, and the country began to recuperate. The port of Rosario sprang into being, and the other river cities rapidly doubled in population. But towards the end of Urquiza's term civil troubles were renewed. The Province of Buenos Aires had been left outside the Confederation and was in a position of antagonism to the other Provinces. The party of the capital was called the Porteños--the men of the Port--and they took the place of the old Unitarian party. In 1859 Buenos Aires actually declared war upon the Federal Government, but Urquiza defeated its forces. Before a settlement could be made his term of office expired and he was succeeded by Dr. Durqui. Fortunately, the Governor of Buenos Aires, Bartolemo Mitre, was a true patriot, and though he was obliged to make war upon the President his efforts were directed to settling the Federal question, and they were, for the time, successful. Urquiza evacuated the capital and retired southwards. Mitre followed him with a large army, and in October, 1861, defeated him at Pavon and himself became President. It would have been well if the energies of Mitre had been left unhampered to settle the thorny question of the respective claims of the Porteños and the provincials, but it was the misfortune of Argentina to be suddenly involved in the most serious foreign war of its history. This was the great Paraguayan war. The occasion of the hostilities was Uruguay. That country had long been distracted by the savage political strife of the Colorados and Blancos, and in 1864 the Blancos, having got the upper hand, elected Dr. Aguirre to the Presidency, who, by his rigorous measures against all suspected of disaffection, excited the resentment of both Argentina and Brazil. Both of these countries had important stock-raising interests on the Uruguay frontiers, and in the civil turmoil their subjects were frequently subjected to extortion and plunder. Having incurred the hostility of its too-powerful neighbours, Uruguay looked about for an ally, and found one in General Lopez, the Dictator of Paraguay.