The arms crisis of 1970 and entry to the EEC in 1973 were the most significant events in Irish politics in the second half of the 20th century. One marked the beginning of the end of unquestioned and unquestioning nationalism; the other led Ireland irrevocably into the wider world. The crisis, which Justin O'Brien covers in fine detail, had begun - in separate struggles inside Fianna Fail and the republican movement - long before it came to light in May 1970 when Jack Lynch sacked Charles Haughey and Neil Blaney on suspicion of involvement in a plot to import arms.
And its impact continued to be felt long after a district justice decided that Blaney had no case to answer and a jury in the High Court found Haughey and three others - James Kelly, John Kelly and Albert Luykx - not guilty of conspiring to import arms illegally into the State. The effects were felt in all parties but especially in Fianna Fail, which Lynch had come to lead in 1966, and in the republican movement, whose leaders had already moved to the left and, in line with their pursuit of politics, strongly supported the Northern Ireland Civil Rights Association.
But the crisis and its impact are rarely discussed and have never been fully analysed. Indeed, people in their 20s or 30s may well complain that its origins and outcome are as much a mystery now as the civil war was to their parents in the 1940s and 1950s. O'Brien is at his best on the detail of NICRA's growth and the inept political responses, North and South; on the polarisation of the Northern community which began with the outbreak of violence in 1969 and led, step by sickening step, to disaster.
Disaster was not inevitable, but it would have taken rare qualities of leadership to avoid it, once the Provisional IRA emerged from the ashes of the civil rights movement, and Blaney and Haughey seized the moment for an opportunistic swoop on Lynch's distinctly unfanatical leadership.
Of course, it's arguable that both splits would have happened anyway. It was their combined effect - on politics generally and on each other - that proved so complex and destructive, as is clear from O'Brien's description of a meeting at Bailieborough, Co Cavan which has been described as the genesis of the plot to import arms.
It was October 1969, and the meeting was arranged so that the defenders of Northern Catholics could inform Captain James Kelly of Military Intelligence of their concerns; it turned into a discussion about arming the Northern command of the IRA. Captain Kelly's report began: "The NI Republican movement is now a six-county org. Its present first priority is the acquisition of arms for defensive purposes. It has the finance to accomplish this and it is the intention to import arms through the SOUTH."
But, as O'Brien explains, this was not the only report from Bailieborough. The Special Branch account, which spoke of "money changing hands and heavy drinking" was sent to the secretary of the Department of Justice, Peter Berry. Berry tried but failed (as he often did) to find his minister, Micheal O Morain. So he contacted his former boss, Haughey, who was a member of the cabinet sub-committee on the North. What Berry did not know was that Haughey, as Minister for Finance and dispenser of a grant-in-aid voted by the Dail for the relief of distress in the North, had paid for the Bailieborough meeting.
But there's another twist to the story: on the previous day Haughey had made the British Ambassador, Sir Andrew Gilchrist, an offer. In return for British support for a united Ireland, Britain or NATO could have access to the old treaty ports: "According to Gilchrist, Haughey wanted a secret commitment that the Border would be the subject of an intergovernmental review."
The Arms Trial produces a wealth of such documented detail. There are times, however, when you begin to doubt the author's judgment. Captain Kelly, we're told, "concludes that the only option open to the government was to `co-operate with the IRA and extreme republicans generally'." (This was in August 1969.)
Then there's the intriguing note: "Documents provided to the author make it clear that Military Intelligence himself viewed the displacement of the leading Belfast republican loyal to (Cathal) Goulding as the paramount objective." And what are we to make of the comment on Lynch's announcement that Britain had accepted the government's role as the guarantor of the rights of Northern nationalists: "Lynch subverted the ultimate goal. He was in effect ending the Irish revolution"? O'Brien deserves two cheers for the research, no marks at all for misjudgments like that.
Dick Walsh is an Assistant Editor of The Irish Times