The new ruler was no such determined _doctrinaire_ as Francia. He was rather a clever opportunist than a gloomy idealist. He adopted many liberal measures, such as the law providing that all negroes thereafter born should be free, and he even attempted to frame a regular constitution. He abandoned the policy of isolation, so dear to Francia, and opened the country in 1845. He loved appreciation and especially wished the approbation of foreigners. Though cautious and reluctant to engage in outside complications, he was by nature and taste a diplomat, and he welcomed the opportunity to try his wits in wider competition than Paraguay afforded. In 1844, Rosas, the tyrant of Buenos Aires, was engaged in a contest with revolutionists in Corrientes. His ultimate purpose was manifestly to unite the whole Plate valley under his authority. Lopez shared the uneasiness of other neighbouring rulers at the growth of Rosas's power. The latter promulgated a decree forbidding the navigation of the Parana to any but Argentine vessels. This decree was an attack on Paraguay's very plain and natural right to reach the ocean, and absolutely shut her off from the outside world. Lopez resented the aggression, and after many protests declared war against Buenos Aires in 1849. Nothing came of it, however, except to give his oldest son a chance to see actual service and to emphasise Lopez's enmity to Rosas and his policy. The way was prepared for his friendship with Urquiza, the great leader of the Argentine provincials, and for the opening of Paraguay to foreign commerce. Permission was granted in 1845 for foreign ships to ascend the Paraguay as far as Asuncion, and foreigners were no longer forbidden to enter the country. On the contrary, Lopez evinced a marked desire for their society and encouraged them to come and engage in trade. His manners were engaging and his courtesies untiring, unless his will was crossed or his suspicions aroused, when he could be very unreasonable and arbitrary.