In the late 1500s Ireland was formally turned into a kingdom, but the king was still the English ruler. During this time, from the 1200-1500s Irish law and culture was strongly influenced by the English ruler's ability or willingness to impose English customs on the Irish people, creating numerous resurgences of Irish pride followed by strong English influence. This ended in the late 1500s when the English kings took firmer control over Ireland.
In the 1500s England altered church allegiance from the Catholic Church to the Anglican Church, a move that had great ramifications on the Irish people as the mostly Catholic population was forced to convert or failed to receive many basic rights and freedoms over the next couple centuries. This essentially ended in the late 1700s with a surge in population and the introduction of the Industrial Revolution. This however also encouraged further Irish pride, leading to independence movements, and later the Act of Union, passed in 1800, which, officially united Great Britain and Ireland.
In the 1840s Ireland was struck by the Great Irish Potato Famine, which devastated the population via death and emigration (particularly to the United States). Following this came another great surge in Irish pride, but this time independence from Great Britain was the only true goal. This campaign, led primarily by Irish Catholics, continued into the 1900s, but by then serious resistance had also begun as many Protestants believed an independent Ireland would be controlled by the Catholic majority.
Following delays, brought upon by British and Irish involvement in World War I, these independence movements again grew until Ireland gained the support it needed to form its own country in 1919 (although not all battles ended until 1923). There remained a number of counties that opposed this movement and remained a part of Great Britain, today known as Northern Ireland.