I think 1966 was a turning point. There was a thaw in 'hostilities' during the mid-60s but the commemoration of the anniversary of the 1916 Easter rising and the reaction to it brought the thaw to a shuddering halt.
Also the thaw was seen as a threat to the two aspirations and people like Hume and Paisley took to the streets. Their street politics and the politics of the times elsewhere produced a lethal cocktail.