The Polish populace was by and large brought back into the fold of Catholicism during the first half of the 17th century, but anti-Protestant attacks continued. They most often took the form of written Catholic propaganda pamphlets and strict Church censorship of dissenting views. The one clear instance of active persecution undertaken against a religious minority was the expulsion of the Polish Brethren, who during the Swedish Deluge strongly supported King Charles Gustav. The sejm of 1658 sentenced the so-called Arians to banishment, unless they convert to Catholicism. As a result, several hundred families (about five thousand people) left the Commonwealth in 1660, while others, threatened with capital punishment and confiscations, faked conversion, only to subject themselves to further statutory persecution. The Polish Brethren were among the most enlightened segments of the society and their expulsion had strong deleterious effects on the country's intellectual development. Other Protestant denominations remained, at least formally, protected by the rules of the 1573 Warsaw Confederation. Many Silesian Protestants entered the Commonwealth in order to avoid recatholization in the Holy Roman Empire after the Peace of Westphalia of 1648. Further restrictions however soon followed.