Penal Laws
The "Penal Laws" or "Popery Laws" were established by the Irish Parliament against Roman Catholics in Ireland throughout the 1690s (until 1746). They included laws about religious practices as well as Catholic landownership.
The Plantation of Ulster in 1609 and the successive colonisation of the whole island of Ireland throughout the 17th century caused several conflicts between the native Irish and the dominating Protestant settlers. Two key events in this context which excacerbated the situation were the Irish rebellion (also called the Rising of 1641), which was quelled by Oliver Cromwell in 1649 and the Battle of the Boyne. The Protestant Ascendancy, members of the Protestant Episcopalian church who dominated the native Irish as landowners and in Parliament, were therefore still afraid of potential riots and cosequently initiated laws to ensure the suppression of the Irish Catholics. Enforced under Queen Anne the laws challenged the agreements of the Treaty of Limerick which was signed by William of Orange (Otto 25).
At first Catholics were not allowed to carry any weapons and were excluded from the armed forces. Their children were not allowed to attend school. Furthermore they were not allowed to own a horse worth more than five Pounds. Much more effective were several laws concerning landownership.
Consequences:
"The laws were of vital importance in broadening the differences between the Irish establishment and its opponents [...] Some of these laws, and notably those affecting property, were rigidly enforced, while others were unenforcable. Their main effects were to entrench the divide between Catholics and Protestants" (Darby 15/16).
On the other hand the Catholic Irish continued their religious practices non-publicly.
Sources:
Darby, John. "The Historical Background." Northern Ireland: The Background to the Conflict. Ed. John Darby. Belfast: Appletree Press, 1983.
Otto, Frank. Der Nordirlandkonflikt: Ursprung, Verlauf, Perspektiven. Munich: C.H. Beck, 2005.