On February 25, 1570 Queen Elizabeth I was officially excommunicated from the Roman Catholic Church and declared a heretic, whereupon The English Parliament declared it treason to call the queen a heretic or imply that she was not the rightful monarch. It put English Catholics in a bind: They had to choose between renouncing their faith or facing crippling fines for committing treason.
A decade earlier the English parliament had passed a law that affirmed the Anglican Church's independence from the Roman Catholic Church. Some Catholic European monarchs had wanted to overthrow Elizabeth, but the pope wasn't particularly eager to since she had a record of tolerating Catholics worshipping in private. When Catholic rebellions broke out in northern England and in Ireland, the English government began persecuting Catholics. The pope was forced to excommunicate Elizabeth for ordering this persecution, so the English government started rounding up Jesuit priests and killing them, on the contrived grounds that they were conspiring against England with Spain.
The biased viewpoint of so many Wikipedia articles is well displayed by its coverage of this topic, like so:
https://en.wikipedia.org/wiki/Regnans_in_Excelsis?