Erasmian humanism paved the way for the spread of the Protestant Reformation in the Swiss Confederation. Basel’s printing houses played a major role in the diffusion of Luther’s ideas, which were then further disseminated by preachers in other cities. Supported by Zurich’s ruling council, Huldrych Zwingli played a key role in spreading the Evangelical movement in Switzerland. Anabaptism also attracted many adherents, but persecution effectively marginalised the movement and limited it to rural areas. Central Switzerland remained staunchly Catholic, and a brief war broke out between Catholic and Protestant Confederates in 1531. The resulting Peace of Kappel rolled back the progress of reform and created a bi-confessional structure within the Confederation. The Catholic cantons formed a majority but they were countered by the powerful Reformed cities of Zurich, Basel, Bern and Schaffhausen. Through the second half of the century these cities allied with Geneva and developed a strong Swiss Reformed identity in response to both German Lutherans and the Tridentine Catholicism that spread from Italy. Confessional tensions were particularly marked in areas jointly governed by Protestant and Catholic members of the Confederation, but competing religious loyalties were never strong enough to overcome their shared political identity as Swiss.