WI:A Terrible and Immediate War-The Irish Republican Army unite and reject the treaty

The Irish Civil War began when the Irish Republican Army split along the lines of ratifying the Anglo-Irish treaty and renewing the war. The IRA delegation was promised the renewal of 'terrible and immediate war' by Lloyd George. So what happens if the IRA reject the treaty outright, a more radical delegation perhaps, what lengths would the British actually go to, and what would the end result be?
 
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