"The Troubles" were a thirty-year period from 1968 to the Peace Accords in 1998 that were marked by sectarian violence in Northern Ireland. In researching this time period, you might want to concentrate on the issues involved, which was mainly the constitutional status of Northern Ireland. The Protestants in Northern Ireland were unionists, meaning that they wanted to remain part of the United Kingdom. The Catholics (who were in the minority) were republicans, meaning that they wanted to join the Republic of Ireland. While "The Troubles" had a religious element, it was not a religious war. Instead, the Catholic minority felt that the Protestant government made them have an inferior position with regard to housing, jobs, and other issues.
You might also want to concentrate on the unfortunate violence between the two sides. In 1969, the British government sent troops to Northern Ireland in response to riots, and in 1972, they revoked the right of the parliament of Northern Ireland to govern and ruled Northern Ireland directly from London. The Irish Republican Army (IRA), a paramilitary group in Northern Ireland (originally the Provisional Irish Republican Army), tried to use military action to force the British to withdraw from Northern Ireland. The Protestants also had paramilitary organizations, including the Ulster Defense Force (UDF) and Ulster Volunteer Force (UVF), also committed to using military force.
There were periods of great violence. For example, in 1972 alone, over 500 people died in the conflict. You might examine claims and counterclaims about the source of this violence. The unionists blamed the IRA, while the nationalists blamed the violence perpetrated by the British Army in events such as the Falls Curfew in 1970, when the British Army tried to sweep Belfast in search of weapons and wound up fighting gun battles with the IRA and imposing a curfew in the area.
In addition, you should focus on the different accords that were created to try to resolve the crisis. The Sunningdale Agreement in 1974 created a government that had different constituents and power sharing, as well as a role for the government of Ireland, but it failed after a strike by the Ulster Workers' Council. The Anglo-Irish Agreement in 1985 allowed the Republic of Ireland to have a role in the government of Northern Ireland, but it was opposed by Sinn Fein, the political organization that was associated with the IRA. Finally, the Good Friday Agreement, the negotiations for which began in 1996, was implemented in 1998 with the return of self-government to Northern Ireland and a situation of power-sharing among different groups.