Though some issues had been festering for several decades, or longer, the main culprit of the division between “old” Catholics and Roman Catholics was the Roman dictate in 1870 of “papal infallibility”. The following is from http://www.bbc.co.uk/religion/religions/christianity/pope/infallibility.shtml -
Infallibility of the Pope
Though papal infallibility was only set in stone in 1870, the idea had been part of church history and debate as far back as 519 when the notion of the Bishop of Rome as the preserver of apostolic truth was set out in the Formula of Hormisdas. In 1075 Pope Gregory VII in his Dictatus Papae (The Pope's Memorandum) put it more bluntly. He set out 27 propositions about the powers of the office of Bishop of Rome. These included the statement that the papacy "never will err to all eternity according to the testimony of Holy Scripture". The word infallibility, however, was not used. It was believed that only God was infallible and it was acknowledged that various popes down the ages had brought disgrace on the office by their behaviour and judgements. Moreover, papal teaching authority was not seen as being wholly independent of councils of the church. No major controversy in the first thousand years of Christianity was ever settled simply by papal decree. It was not until the nineteenth century that moves began to make a formal acknowledgement that the pope was infallible. It was seen as a useful tool in the Church's rejection of the liberal, secular agenda that was sweeping Europe. Having been dethroned as ruler of the Papal States by the movement for Italian Reunification that finally triumphed in 1870, Pope Pius IX called the First Vatican Council where he was determined to buttress his own spiritual authority. Though many cardinals believed it dangerous to try to define quite how and when the Pope might speak infallibly, a compromise agreement was finally reached. It stated that Pope "when he speaks ex cathedra, that is when exercising the office of pastor and teacher of all Christians" is "possessed of infallibility" when "he defines... a doctrine concerning faith and morals to be held by the whole Church, through the divine assistance promised to him by St Peter".