The war against the castles had another bad effect. It involved the cities in a long succession of mutual wars, which have given origin to the theory, till lately in vogue, namely, that the towns lost their independence through their own jealousies and mutual fights. The imperialist historians have especially supported this theory, which, however, is very much undermined now by modern research. It is certain that in Italy cities fought each other with a stubborn animosity, but nowhere else did such contests attain the same proportions; and in Italy itself the city wars, especially those of the earlier period, had their special causes. They were (as was already shown by Sismondi and Ferrari) a mere continuation of the war against the castles--the free municipal and federative principle unavoidably entering into a fierce contest with feudalism, imperialism, and papacy. Many towns which had but partially shaken off the yoke of the bishop, the lord, or the Emperor, were simply driven against the free cities by the nobles, the Emperor, and Church, whose policy was to divide the cities and to arm them against each other. These special circumstances (partly reflected on to Germany also) explain why the Italian towns, some of which sought support with the Emperor to combat the Pope, while the others sought support from the Church to resist the Emperor, were soon divided into a Gibelin and a Guelf camp, and why the same division appeared in each separate city.(19) The immense economical progress realized by most italian cities just at the time when these wars were hottest,(20) and the alliances so easily concluded between towns, still better characterize those struggles and further undermine the above theory. Already in the years 1130-1150 powerful leagues came into existence; and a few years later, when Frederick Barbarossa invaded Italy and, supported by the nobles and some retardatory cities, marched against Milan, popular enthusiasm was roused in many towns by popular preachers. Crema, Piacenza, Brescia, Tortona, etc., went to the rescue; the banners of the guilds of Verona, Padua, Vicenza, and Trevisa floated side by side in the cities' camp against the banners of the Emperor and the nobles. Next year the Lombardian League came into existence, and sixty years later we see it reinforced by many other cities, and forming a lasting organization which had half of its federal war-chest in Genoa and the other half in Venice.(21) In Tuscany, Florence headed another powerful league, to which Lucca, Bologna, Pistoia, etc., belonged, and which played an important part in crushing down the nobles in middle Italy, while smaller leagues were of common occurrence. It is thus certain that although petty jealousies undoubtedly existed, and discord could be easily sown, they did not prevent the towns from uniting together for the common defence of liberty. Only later on, when separate cities became little States, wars