Ephemeral unity therefore, after the Ghihellina one, also this papal, Angevin, Guelph unity. Ephemeral, as a unit of domination or political control over the whole peninsula. But both are important as an index and cause of common elements of life, common tendencies and passions and thoughts, from the Alps to Sicily; as an index and cause of corrosion and relaxation of municipal institutions and spirits.
This phase of Italian life, marked by the papal, Guelph and Angevin prevalence, is also a phase of great development of mercantile and banking activities, especially in municipal Italy. Guelphism is often the prevalence of interests aimed at commerce and the bank, which find greater defense and impetus in it. In the shadow of its flag, and in the conditions it creates on the peninsula, the cities that have the greatest capacities and economic possibilities now prevail over the others. Venice, which in the 13th century turned more attention to the things of its nearby mainland and encountered obstacles in the incipient aristocratic formations of the Salinguerra and Ezzelinos in Ferrara, Padua, Treviso, Verona; Venice now finds in the struggle against Ghibellinism an excellent opportunity to hasten the ruin of those uncomfortable neighbors. Placed on the fringes of Italian life, Venice begins to link itself to it with very notable political and commercial ties. In this period, the links between Lombardy and the ports of the Adriatic have also multiplied, especially with Venice; even more, those with Genoa. In the 13th century Genoa became a highly sought-after outlet for the Piedmont region and also for Bologna; but it is, more truly, almost a port of Milan, as Bonvesin della Riva calls it. Already between the 12th and 13th centuries there was a large colony of Milanese merchants. Among other things, Milan has almost acquired the monopoly of the arms trade. Communications through Alessandria and Tortona with Liguria and France; those with Tuscany for the Parma and Piacenza Apennines; with Germany for Como, Val di Blenio, Val Leventina, Valtellina, Milan takes care of and defends them by any means, wars or treaties. Claims on Federico II and the Comaschi Val di Blenio and Leventina. It takes away Bellinzona from Como, the outlet of those valleys in the Verbano. The lordship of the Torriani is the defense of the Milanese trade inside and out, against the nobility and lords of the Po Valley. The latter, however, are also concerned with the mercantile interests of their city, as shown by the example of Salinguerra in Ferrara and Pelavicino in the center of the Po Valley.
In Tuscany there is even more economic movement that gives the region a certain discordant unity and from there it radiates widely around. The whole country, especially the Valdarno, gravitates towards Pisa for the port, which unites and divides those cities. But from the mid-thirteenth century onwards, Florence took a leap at the head of the region. The Guelph wars against the Ghibelline Pisa push the municipalities of the Tuscan Taglia Guelfa, headed by Florence, to use the port of Genoa, an ally against the Pisans. Almost all the municipalities of Tuscany have agreements and treaties with Genoa. No less than the Genoa road, Florence knows that of Venice, through the vast world. Venetian and Florentine houses work together there, for companies from Puglia and the East, where Venetian exports will soon face competition from Florentine industries. in terms of pannilani and silk. And probably the starting point of those many Florentine families that soon begin to appear in the cities of Croatia and Dalmatia, Salviati, Altoviti, Giacomini, etc., is Venice. With Venice and Padua and the cities of the Marca Trevigiana, as with Genoa and Modena and Reggio and Parma and Cremona and Milan, Florence had, between 1270 and 1280, a series of commercial treaties. Up to the north-east corner of the peninsula, Friuli and the patriarchate are immigration destinations for Florentine, Sienese, Locchese and Pisan families, which reached its highest point in the second half of the 13th century. It is also determined by the struggles of the parties and by the exiled convicts: but it is aimed at essentially economic activities. The Tuscans were added or replaced, around 1270, by Lombards, clerics and seculars, friends and spouses following Raimondo della Torre, former bishop of Como, now patriarch of Aquileia. His house becomes a hearth and a point of radiation of Lombardi towards the Istrian cities. Un della Torre is also the first mayor of Trieste, in 1293.
According to itypemba, Guelph politics second and also promotes the relations of Florence with Bologna and Romagna, land of the Church, for the Ombrone-Reno, Sieve-Lamone valleys. Faenza is an important outlet on Romagna. Between Florence and Bologna there are even, in the 13th century, pages of common history, as regards the struggles against the Ghibelline side, the emancipation of the serfs, the laws against the magnates: by now the ancient barrier between Longobard and Byzantine Italy is not exists more. The new and proper life of the cities has destroyed it. And also the feudal world of Tuscany and Romagna are one thing: an object of concern for the popes, who want to be masters in Romagna; and also, for them, an incitement to give political unity, papal unity, to the lands of Tuscany and Romagna. The economic relations of Florence are even more resentful of the Guelph victory of 1266, and also of Venice, with southern Italy. The gates of the kingdom now truly open wide. If Charles, from there, works to politically dominate Tuscany and the Po Valley, the kingdom and the king’s court fall under the influence of the trade and finance of the north, especially of Florence and Venice.