Pope Gregory X. was highly displeased by this war, and by the ardour and pertinacity with which it was pursued, for he considered the Ghibelline spirit of Pisa a barrier to the growing power of the Florentines, who, in spite of being Guelphs, used every effort to become wholly independent of the Papacy. Wherefore, after vainly enjoining them to put an end to the war, he excommunicated their city. But the Florentines offered slight excuses, and until 1276 paid no attention to his thunders. Then at last peace was declared, but during its very brief duration plans were arranged for new expeditions. After this the Republic of Pisa enjoyed a few tranquil years, and owing to the vastness of its trade and the extension of its colonies, its finances were rapidly restored to their former prosperity. Unfortunately, certain Pisan families had become so powerful by means of their wealth that, no longer satisfied with republican equality, they sought to dominate the internal affairs of the State and direct its foreign policy in favour of their personal ambition rather than of the interests of the State. The Judges of Gallura and Arborea, Counts Ugolino, Fazio, Neri, and Anselmo della Gherardesca, all had their own little courts and men-at-arms after the fashion of princes. Absorbed in covetous rivalries, they distracted the attention of the magistrates from the dangers threatening their republic, and daily becoming graver and more imminent. For, in fact, the strength of the Republic was not only almost exhausted by the continuous attacks of the Guelph League, but for some time past the rivalry of Genoa had been threatening to culminate in a still deadlier strife. As both these maritime cities were Ghibelline, they had every reason to be at peace with each other and combine in defending their interests against the far greater sea power of Venice. But, on the contrary, this only seemed to exasperate their reciprocal jealousy. Their fleets were constantly in collision in Levantine waters. They had a desperate encounter in 1277 near Constantinople and on the Black Sea. It ended in disaster for the Pisans, who had been the assailants, and from that moment they panted for revenge. Nor were opportunities lacking. While the Venetians were asserting absolute dominion over the Adriatic, the Genoese and Pisans, hard by on the Mediterranean, were always crossing each other's tracks, inasmuch as both were engaged in the same trading ventures, and both possessed colonies in the same islands of Corsica and Sardinia. Thus, they were involved in continual conflict. Then, too, as the Guelph League was specially hostile to Pisa, it supplied Genoa with perpetual pretexts for beginning the hostilities which the Florentines were seeking to incite by every political manoeuvre. At last their reciprocal hatred reached so high a pitch that the Pisans themselves were the first to provoke the war. Their burning desire for reprisals