It is known italian clergy was radically against Spanish influence pushed during Trent's Council (basically cardinal Cisneros' religious reform in Spain forced upon the whole Catholic Church). This hostility came from long before, from the Aragonese conquest of Naples which caused a mass scale anti-Spanish reaction among the many italin states during XVI century that did led to several anti-Spanish uprise in Rome and north italian cities.

Theology largelly served as a weapon used by nationalism during XVI and XVII centuries, Luther in Germany, Loyola in Spain, etc. The Napolitan pope Paul IV denouced Spanish presence in Naples, Sicily and Milan, while also denounced Spanish Church a bunch of heretics waiting to show their true face, he didn't trust the Jesuits neither (who he considered an Spanish army dressed with togas), he had a bad opinion about Loyola and much worse about Loyola's succesor, Diego Laínez who played a keyrole at Trent's Council.

In fact, when pope Clement VII rebelled against Charles I, V for Germans, setting a path followed by posterior popes such as Carafa, the very schism of English Church did happen due Charles pressing the pope to decline Henry VIII demands to divorce Catherine of Aragon.

Following this declinign by late XVI century Italic trend as well, the Catholic Venetian friar, Paolo Sarpi, who was highly critical with Trent Council, Jesuits and Habsbourgs, wrote in is work "History of the Council of Trent (1619)" all the things he disagreed with the Council, a best-seller among Protestants in Northern Europe.

What if Trent's Council never happened, how possible could have been a reunification between Protestant congregations with Rome?