The agreement was approved by voters across the island of Ireland in two referendums on 22 May 1998. In Northern Ireland, in the 1998 referendum on the Good Friday Agreement in Northern Ireland, voters were asked if they supported the multi-party agreement. In the Republic of Ireland, voters were asked whether they would allow the state to sign the agreement and authorize the necessary constitutional changes (nineteen constitutional amendments from Ireland) to facilitate it. The citizens of both countries had to approve the agreement to implement it. 12. Any change in these provisions, in agreement with the Council and with the express approval of the Northern Ireland Assembly and the oireachtas, subject to the scope of the powers and responsibility of both administrations. As part of the agreement, the British Parliament repealed the Government of Ireland Act 1920 (which had founded Northern Ireland, divided Ireland and asserted territorial right to the whole of Ireland) and the people of the Republic of Ireland amended Articles 2 and 3 of the Irish Constitution, which asserted a territorial right to Northern Ireland. The main themes addressed by Sunningdale and dealt with in the Belfast Agreement are the principle of self-determination, the recognition of the two national identities, intergovernmental cooperation between the British and Ireland and legal procedures for compulsory power-sharing, such as inter-community voting and the D`Hondt system for appointing ministers to the executive.   Former IRA member and journalist Tommy McKearney says the main difference is the British government`s intention to negotiate a comprehensive agreement including the IRA and the most intransigent unionists.  With regard to the right to self-determination, two qualifications are recorded by the writer Austen Morgan.
First, the transfer of territory from one state to another must be done through an international agreement between the British and Irish governments. Second, the population of Northern Ireland can no longer be alone in united Ireland; They need not only the Irish government, but also the people of their neighbouring country, Ireland, to support unity.