The Reformation was one of the most important schisms or divisions in Christianity, the other major schism being the split between Roman Catholicism and the Eastern Orthodox Church Christians. Basically the Roman Catholic Church had become very corrupt and Martin Luther thought the pope was unfit to rule. So Luther founded Protestantism.
Now in the 21st century quite a number of people in Ireland and elsewhere think the Roman Catholic Church is corrupt and the pope is unfit to rule. Some are leaving the RC church to join other Christian sects or occasionally become secular while others stay in the RC's but don't fully accept the authority of the church. The Roman Catholics are in deep trouble and the outcome is uncertain.