"Why did the Church condemn the Fenians exactly? What were the specific reasons?"
It's a perfectly good question.
Here's why: the Fenians were a parcel of revolutionaries hell-bent upon overthrowing the established order in Ireland - including the clergy - and bringing in a secular republic guided by principles based upon the anti-Catholic French Revolution and upon a form of incipient Communism.
They expressly eschewed the non-violent approach to reform of Daniel O'Connell and deliberately opted for violence and murder of the innocent, particularly police officers.
In short, they were a gang of heathen thugs and murderers.
Bishop David Moriarty of Kerry said of the Fenian leaders (and I quote) that they were:
"criminals, swindlers" and "God's heaviest curse" and "deserving damnation" adding that "eternity is not long enough, nor hell hot enough" for their kind.
I should add that Bishop Moriarty was an Irish patriot. However, he objected to swindlers and murderers.
Here is what Lawrence John McCaffrey says in his book The Irish Catholic Diaspora in America (1976), page 150:
"...next to the British government, the Catholic Church in Ireland was the leading foe of Fenianism. Bishops denounced the IRB as a secret, oath-bound society, and denied the sacraments to its known members...[Cardinal] Cullen [the Archbishop of Dublin] and his fellow prelates were also frightened by the violent rhetoric and strategy of the IRB, believing that the group's inspiration came from Giuseppe Garibaldi-style continental, anti-Catholic, radical nationalism and the egalitarian and violent mood of urban America...Cardinal Cullen decreed that no Catholic church in his archdiocese could be used for any religious ceremony that might be construed as an honour to revolutionary nationalism."
Here is what Oliver Rafferty says in his book Catholicism in Ulster, 1603-1983: An Interpretative History (1994) at pages 162-4:
"A more important and decisive intervention in Irish political affairs was the condemnation of Fenianism 'by name' issued by Pius IX in January 1870...[Cardinal Cullen] called a meeting of the bishops, then all in Rome for the First Vatican Council, and persuaded them in the interests of religion to petition the Holy See for a condemnation of the Fenians. All the Ulster bishops voted in favour of the petition. Pius IX duly obliged and the decree condemning Fenianism was issued at the end of January 1870."
In fact, the decree was a clarification, ordered by Blessed Pope Pius IX to be issued in case there were any doubt that his earlier decrees, including Apostolicae Sedis Moderationi, meant to condemn the Fenians specifically. It was issued on 12 January 1870 by the Roman Inquisition on the direct order of Blessed Pope Pius IX. Here is what it says:
"As it may be doubted by many whether the society of Fenians is included and denounced among the societies condemned in the Pontifical Constitutions, our most Holy Father Pius IX, having first taken the opinions of the eminent cardinals, the inquisitors-general appointed to guard against heretical perversity in the universal Christian republic, lest the hearts of the faithful, particularly the simple, should be perverted, to the imminent danger of their souls, and adhering to the decrees of the congregation of the General Inquisition issued in like circumstances, especially the decree of 5 July 1865, has decreed and declared that the American or Irish society called Fenian is comprised among the societies forbidden and condemned in the Constitutions of the Supreme Pontiff, and in particular by that lately issued by his Holiness, dated 29 October 1869, beginning Apostolicae Sedis in paragraph 4 of which are declared liable to sentence of excommunication, to be removed only by the Pope, 'those sects called Freemasons, Carbonari, or any other kinds of sects which either openly or privately plot against the Church or legitimately constituted authorities, together with those who in any way favour the same; as also their secret heads or leaders, so long as they shall not have denounced them.' He has, therefore, commanded this answer to be given to certain bishops who have asked the question.
Notary of the Holy Roman Inquisition
12 January 1870"
Apostolicae Sedis Moderationi was a papal bull issued by Blessed Pope Pius IX on 12 October 1869 which revised the list of censures that in canon law were imposed automatically (latae sententiae) on offenders. It reduced their number and clarified those preserved. Of the total of 45 censures, one (the fourth among those for which absolution was reserved to the Pope, but not in a special manner) was directed against membership of "Freemasonry, the Carbonari and similar groups".
Some sought to excuse the Fenians from being condemned by this and earlier papal bulls and so Blessed Pope Pius IX ordered the clarification quoted above so that there could be no doubt. He did this at the invitation of the Irish bishops, led by Cardinal Cullen.
Any objective person considering the revolutionary violence espoused by, and practiced by, the Fenians and the IRB can be in no doubt whatsoever that they fully deserved this condemnation. The Fenians and IRB made no bones about committing plain, outright murder to try to get their way.
Since murder is a sin that cries to heaven for vengeance, as the Catechism teaches us, there can be little doubt that unrepentant Fenians and IRB members were in obvious and mortal danger of Hellfire. All Catholics needed to be told this and Blessed Pope Pius IX did not shrink from the task.
The term "Fenian" is an umbrella term used to describe both the Fenian Brotherhood, founded by American John O'Mahoney, and the Irish Republican Brotherhood (originally called the Irish Revolutionary Brotherhood), founded by James Fitzjames Stephens on 17 March 1858 in Lombard Street, Dublin, together with Thomas Clarke Luby, John O'Leary and Charles Kickham.
Both organisations were consciously modelled on the ideas of the French Revolution and the Irish tricolour flag was even brought over to Ireland from revolutionary France by Thomas Francis Meagher for that very reason.
Be in no doubt: the tricolour is an anti-Catholic, revolutionary flag - or, more properly, rag. It deliberately eschews anything resembling the Christian cross.
Generations of Irishmen have been swindled into believing otherwise.
Both organisations were secret societies with secret, blood-curdling oaths, and they were dedicated to the establishment of an independent, secular Irish republic by violence, murder and mayhem.
O'Mahoney expressly claimed that Irish independence could only be obtained by armed revolution. He was, in effect, an early Communist. Stephens was, if anything, even more openly Communist in his views.
O'Mahoney even managed to help orchestrate the Fenian invasions and raids of Canada from the USA between 1866 and 1871. These raids, which were designed to take over parts of Canada and then try to pressure or blackmail the British government, all failed and ensured that Irish-Canadians ceased to have any sympathy for the Fenians, if they ever had any. It also engendered much anti-American feeling since the American government did little to stop the Fenians using US territory to mount the raids.
Both Stephens and O'Mahoney had participated in the failed 1848 "Young Ireland" rebellion which Dan O'Connell had roundly condemned. The "Young Irelanders" expressly split from O'Connell precisely because he refused to countenance any violence.
In 1867 three Fenians - William Allen, Michael O'Brien and Michael Larkin - attacked a police van trying to release captured Fenian criminals. In so doing they murdered policemen. For this they were later tried and hanged at Salford. The backlash against these violent criminals set back the cause of Irish Home rule by decades. Their murders achieved nothing but grieving widows, a growing hatred of Irish politics and a diminishing of the prospects for Home Rule.
The stark reality is that the peaceful, constitutional campaigns of Dan O'Connell which, a generation earlier, had achieved so much including land reform, Catholic emancipation throughout the British Empire and material assistance for the poor, was gravely prejudiced by the stupid and irrational violence and murders committed by the Fenians.
Home Rule, which could have been achieved in the early to mid-19th century, was set back half a century by the rash and senseless acts of violence of these Fenian terrorists, fanatics and murderers.
The Phoenix Park murders on 6 May 1882 of the Chief Secretary for Ireland, Lord Frederick Cavendish and the Permanent Under-Secretary, Thomas Henry Burke, thoroughly scuppered Home Rule for Ireland since Gladstone's minister, Lord Hartington, was Cavendish's elder brother. He split from Gladstone's Liberal Party, and went on to help form the Liberal Unionist Party, so that the Home Rule Bills of 1886 and 1893 failed.
These atrocious murders of innocent men in Phoenix Park served only to put the cause of Home rule back decades and to cause senseless suffering to the families of the victims. Such are the cankered and hateful fruits of Fenian fanaticism, terrorism and murder.
It was only the long, hard, arduous, dedicated and, above all, peaceful and constitutional continuance, by John Redmond and John Dillon, of O'Connell's campaigns that finally resulted in the Irish Home Rule Act in 1914.
The Phoenix Park murderers, Joe Brady, Michael Fagan, Thomas Caffrey, Dan Curley and Tim Kelly, were all convicted and hanged. They belonged to an obscure off-shoot of the Fenians called the "Irish National Invincibles".
Thus did the Fenians and their allies hopelessly set back the cause of Irish Home Rule by their murders, violence and acts of hatred.
The Fenians and the IRB eventually turned into Sinn Fein and the IRA, both murderous organisations which have continued to massacre the innocent right up until the present day.
In case anyone is in any doubt that the modern IRA has not been openly in favour of murder, here is a reminder from Martin McGuiness, who, although now a Cabinet minister in Northern Ireland, has been an openly defiant apologist for killing the innocent. Such a man should automatically be excluded from the government of any civilised nation.
Here is an interview with IRA leader, Sean Mac Stiofain, who boasts about murdering the innocent. Ironically, Mac Stiofain was in reality English-born, with an Irish mother, and was baptised John Stephenson.
Here is an even more disgusting individual, Dan Breen.
An IRA member in the 1919 rebellion, this scoundrel openly boasts of murdering innocent people even to saying that he "makes no apology for killing...and murder" and deceitfully pretends that "all killing is murder". He is a particularly nasty example of the moral poison that was, and still is, Fenianism:
He is not sorry for the murders he committed or, as he puts it, "rubbing them out", even though he is in the "evening of his life". In this clip he remains an unrepentant murderer, boasting of his murders.
But he even tells us who his real "gods" were, namely his fellow terrorists like Michael Collins. And his earlier heroes, Wolfe Tone and Robert Emmet, were both revolutionary Protestants. Wolfe Tone was a suicide who cut his own throat in prison with a razor blade rather than face the gallows.
This man, Dan Breen, was very far from being a Catholic.
He was not even remotely Christian. He was a deep heathen and a violent, murderous revolutionary. He was the very worst sort of person to claim to represent Ireland, a land of Christian saints and scholars. He was the very enemy of true Irishmen and the real Ireland - a shocking criminal, God help him, but a typical representative of the evil genius of Fenianism.
He is also an example of how many of the Fenians were sympathisers with Nazism.
Breen published an account of his guerrilla days, My Fight for Irish Freedom, in 1924. He represented the Tipperary constituency from the fourth Dáil in 1923 as a "Republican", along with Éamon de Valera and Frank Aiken. He became the first anti-Treaty TD actually to take his seat in 1927 but was defeated in the June 1927 general election and decided to travel to the United States. He returned to Ireland and regained his seat as a member of Fianna Fáil in the Dáil at the 1932 general election.
During World War II he was known to hold largely pro-Axis (i.e. Nazi) views.
According to some, in 1948 an Irish-American visited Breen and was shocked to see two pictures of Adolf Hitler on the wall of Breen's study.
After hearing these appalling villains, it must be clear to any sane human being that the whole Fenian, IRB, Sinn Fein and IRA movement is disgraceful, criminal and immoral and thoroughly deserving of the highest possible condemnation by all men, whether religious or not, whether Irish or not.
It is a movement inspired by Hell itself, as Roman Catholic Bishop David Moriarty rightly stated.