Although the Irish Free State was created in 1922 it was not until 1948 that Ireland seceded from the United Kingdom and declared itself the Republic of Ireland. The new Irish Constitution had words to the effect that the declaration was a move towards the dissolution of the division of Ireland. These were merely words and the separation continues still today.
Derry became a flashpoint for what was happening all over the North. The British became so skillful at gerrymandering elections, that although Derry was two-thirds Nationalists, and the vote followed those lines, two thirds of the seats were going to the Loyalists.
On January 30, 1972, a peaceful rally was organized in response to the unjust internment of Irish people. The British could jail innocent people, without bringing formal charges, or being given the right to a trial. People could be jailed for an indefinite period of time. The unarmed protesters were first met with British baton charges and then were gunned down by a Parachute Regiment. In the end 13 people were murdered, all unarmed, all Catholic.
The Protestants were so unyielding that for over 20 years, they made no reforms. The voices and the wishes of the Catholic majority, no matter how small, were totally overlooked. That allowed the situation to degrade to its lowest level - street violence. Times had reached an all time low in Northern Ireland, and the international community was watching.
The international press and many foreign governments panned the British. Support for the British involvement in Northern Ireland was waning fast even in Britain. Even Paul McCartney was so moved by these events, he wrote the hit single 'Give Ireland Back to the Irish.
In order to better understand the 'problems' as they are often called in Northern Ireland, you will have to recognize different sides of the dispute. Although there are many political parties in Ireland, there are basically two different sides; Unionists and Nationalists. The Republic of Ireland is about 95% Catholic and vastly Nationalist. Northern Ireland is about half Protestant and half Catholic. The political leanings follow along those lines.
The Loyalists are typically Irish by birth, Protestant by religion, of British/Anglo Ancestry. They favor remaining part of the United Kingdom. These people are commonly the descendants of English and Scottish people whom were part of the plantation of Ireland (often referred to as planters).
The Nationalist are typically Irish by birth, Catholic by religion, and of Irish/Celtic ancestry. They favor a free and united Ireland. These people are generally the indigenous (native) people of Ireland.
Although the Unionist and Catholics both oppose the others political views many Loyalists take the dispute one-step further. Religion is unfortunately often used to distinguish ones political leanings in Ireland. However, the Catholics by and large have no animosity toward the Protestant faith. On the other hand many Loyalists have a deeply rooted bigotry toward the Catholic Religion.
This is the reason why sectarianism (religion) has become the line of separation in Ireland. Simply put, your religion in Ireland is often indicative of your politics. If you are a Catholic you are thought of as a being a Nationalists who favors a united Ireland. If you are a Protestant you are thought of as a Unionist who wishes for Northern Ireland to remain part of the United Kingdom.