As with most civil wars, the internecine conflict left a bitter legacy, which continues to influence Irish politics to this day. The two largest political parties in the republic through most of its history  were Fianna Fáil and Fine Gael, the descendants respectively of the anti-treaty and pro-treaty forces of 1922. Until the 1970s, almost all of Ireland's prominent politicians were veterans of the Civil War, a fact which poisoned the relationship between Ireland's two biggest parties. Examples of Civil War veterans include: Republicans Éamon de Valera, Frank Aiken, Todd Andrews, and Seán Lemass; and Free State supporters W. T. Cosgrave, Richard Mulcahy and Kevin O'Higgins. Moreover, many of these men's sons and daughters also became politicians, meaning that the personal wounds of the civil war were felt over three generations. In the 1930s, after Fianna Fáil took power for the first time, it looked possible for a while that the Civil War might break out again between the IRA and the pro-Free State Blueshirts. Fortunately, this crisis was averted, and by the 1950s violence was no longer prominent in politics in the Republic of Ireland. However, the breakaway IRA continued  to exist. It was not until 1948 that the IRA renounced military attacks on the forces of the southern Irish state when it became the Republic of Ireland. After this point, the organisation dedicated itself primarily to the end of British rule in Northern Ireland. The IRA Army Council still makes claim to be the legitimate Provisional Government of the Irish Republic declared in 1918 and annulled by the Anglo-Irish Treaty of 1921.
Question: Who did they fear would start another civil war?
Answer: IRA; the IRA