In April 1916, Irish republicans launched the Easter Rising against British rule and proclaimed an Irish Republic. Although it was crushed after a week of fighting, the Rising and the British response led to greater popular support for Irish independence. In the December 1918 election, republican party Sinn Féin won a landslide victory in Ireland. On 21 January 1919 they formed a breakaway government (Dáil Éireann) and declared Irish independence. That day, two RIC officers were killed in the Soloheadbeg ambush by IRA volunteers acting on their own initiative. The conflict developed gradually. For most of 1919, IRA activity involved capturing weaponry and freeing republican prisoners, while the Dáil set about building a state. In September, the British government outlawed the Dáil and Sinn Féin and the conflict intensified. The IRA began ambushing RIC and British Army patrols, attacking their barracks and forcing isolated barracks to be abandoned. The British government bolstered the RIC with recruits from Britain—the Black and Tans and Auxiliaries—who became notorious for ill-discipline and reprisal attacks on civilians, some of which were authorised by the British government. Thus the conflict is sometimes called the "Black and Tan War". The conflict also involved civil disobedience, notably the refusal of Irish railwaymen to transport British forces or military supplies.