Sinn Féin (.nʲ fʲeːnʲ, Mi) is a political party and national movement of Irish Republicanism in the Republic of Ireland and Northern Ireland (which is part of monarchist Great Britain). He advocates the unification of one Republic of Ireland. The roots of the movement lie in the Irish cultural revival from the end of the 19th century and the growing dissatisfaction with the movement for constitutional self-government of Ireland within the British Empire. It was founded by Arthur Griffith in 1900. He was known for founding the national newspaper The United Irishmen in 1899, in which he advocated national self-determination. The movement was not initially explicitly political, nor did it advocate violence. He advocated passive resistance to everything that was considered English and the reintroduction of the Irish language into the everyday speech of Irish people.
In 1905, Sinn Fein was organized as a political movement, but was weak until the beginning of the First World War. The cruel British suppression of the Easter Uprising of 1916 prompted its strengthening. In 1917, several of its leaders, released from prison, reorganized under the leadership of Emon De Valera. In the 1918 election, Sinn Féin ran for all the seats elected in Ireland for the British Parliament, and won 73.
However, due to the protest against the British government over Ireland, the elected representatives did not go to Westminster. Instead, they convened the Irish Assembly in Dublin, called Dáil Éireann, which declared Ireland's independence. Shortly afterwards, the Anglo-Irish War broke out, with British authorities trying to quell an uprising for independence led by Michael Collins. For that, they also used paramilitary formations such as Black and Tens. The cruel attitude of the British authorities enabled Sinn Fein to gain even greater support.
The war ended in 1921 with an agreement according to which Ireland was divided into British Ulster and the Free State of Ireland. The division was opposed by the militant wing of Sinn Fein, led by De Valer, so there was a civil war between supporters and opponents of the Anglo-Irish agreement. In time, most Irish people joined the government, and Sinn Féin himself began to weaken, especially when De Valera left him and entered the assembly in 1927.
In 1938, several movements in the Shin Fein tradition merged with Ireland