the Dutch regions, Philip II of Spain, felt it was his duty to fight Protestantism and, after the wave of iconoclasm, sent troops to crush the rebellion and make the Low Countries a Catholic region once more. The Protestants in the southern Low Countries fled North en masse. Most of the Dutch Protestants were now concentrated in the free Dutch provinces north of the river Rhine, while the Catholic Dutch were situated in the Spanish-occupied or -dominated South. After the Peace of Westphalia in 1648, Protestantism did not spread South, resulting in a difference in religious situations. Contemporary Dutch, according to a 2017 study conducted by Statistics Netherlands, are mostly irreligious with 51% of the population professing no religion. The largest Christian denomination with 24% are the Roman Catholics, followed by 15% Protestants. Furthermore, there are 5% Muslims and 6% others (among others Buddhists). People of Dutch ancestry in the United States and South Africa are generally more religious than their European counterparts; for example, the numerous Dutch communities of western Michigan remain strongholds of the Reformed Church in America and the Christian Reformed Church, both descendants of the Dutch Reformed Church. Cultural divergences One cultural division within Dutch culture is that between the formerly Protestant North and the nowadays Catholic South, which encompasses various cultural differences between the Northern Dutch on one side and the Southern Dutch on the other. This subject has historically received attention from historians, notably Pieter Geyl (1887–1966) and Carel Gerretson (1884–1958). The historical pluriformity of the Dutch cultural landscape has given rise to several theories aimed at both identifying and explaining cultural divergences between different regions. One theory, proposed by A.J. Wichers in 1965, sees differences in mentality between the southeastern, or 'higher', and northwestern, or 'lower' regions within the Netherlands, and seeks to explain these by referring to the different degrees to which these areas were feudalised during the Middle Ages. Another, more recent cultural divide is that between the Randstad, the urban agglomeration in the West of the country, and the other provinces of the Netherlands. In Dutch, the cultural division between North and South is also referred to by the colloquialism "below/above the great rivers" as the rivers Rhine and Meuse roughly form a natural boundary between the Northern Dutch (those Dutch living North of these rivers), and the Southern Dutch (those living South of them). The division is partially caused