According to the Wikipedia article on Calvinism:
Although much of Calvin's work was in Geneva, his publications spread his ideas of a "correctly" reformed church to many parts of Europe. [...] It was influential in France, Lithuania and Poland.
Today, the vast majority of Lithuania and Poland's religious population is Roman Catholic. The protestant minority is, surprisingly, mostly Lutheranism.
The relative insignificance of Calvinist Church in Poland do not appear to be related to the recent atrocities of World War II, as it is clear in the 1931 Polish Census (espcially page 15) that:
- The protestant were already in minority representing a small percentage of Poland's population
- The German speaking population was overrepresented in the Protestant population (about 2/3 of Protestants were Germans, only 1/3 were Poles), which explains why Protestantism lost even more influence in Poland after WWII and the expulsions of Germans (and that in addition to the atrocities targeting specifically Poles's upper class, including of course clerics).
- The vast majority of protestants were Lutherans, including in the Polish-speaking population. It appears that unfortunately the census is particularly confusing among difference trends within Protestantism, but here within protestant only 39% of ethnic Poles and 49% of population declared themselves as other than "Lutheran". So unsurprisingly Germans were mostly Lutherans, what is more surprising is that Poles were also mostly Lutheran.
Going further in the past, back in the Polish-Lithuanian commonwealth, it appears that Protestantism had a much greater influence than today, as it had 8% of the population, and probably a much greater percentage among the nobles (a situation very similar to France at the time, before persecutions against the Huguenots began).
However, since Poland had a long tradition of Religious tolerance, I don't see any sign of significant discrimination against protestants by other non-protestant Poles. My question is: When and why did the influence of Calvinism decrease in Poland?