An ambush party of IRA volunteers acting without orders and led by SeÃ n Treacy attacked a group of Royal Irish Constabulary men . They were escorting a shipment of gelignite to a quarry in Soloheadbeg , County Tipperary . The Irish War of Independence in effect began on the same day that the First DÃ il met on 21 January 1919 , when an ambush party of IRA volunteers acting without orders and led by SeÃ n Treacy , attacked a group of Royal Irish Constabulary men who were escorting a consignment of gelignite to a quarry in Soloheadbeg , County Tipperary .