Quiz -- who said the following?
The American assault on Ireland under the name of Fenianism may be now held to have failed, but the snake is only scotched and not killed. It is far from impossible that the American conspirators may try and obtain in our North American provinces compensation for their defeat in Ireland.
Answer: Lord Palmerston, as Prime Minister, in 1865.
We bring this up because Palmerston has popped up (as he once did for Andrew Sullivan) as an icon of aggressive foreign intervention, this time for Max Boot at the blog of Commentary --
In 1847, David Pacifico, a Jew who had been born in British-held Gibraltar and was therefore a British subject, had his house burned down in Athens by an anti-Semitic mob. The Greek government refused to protect him or provide any restitution. Lord Palmerston, Britain’s foreign secretary, sent the Royal Navy to blockade Greece until it paid Pacifico’s demands.
Critics charged that Palmerston was overreacting. The House of Lords even voted to censure him. But in the House of Commons, Palmerston carried the day with a magnificent five-hour oration in which he declared: “As the Roman, in days of old, held himself free from indignity, when he could say, Civis Romanus sum [I am a Roman citizen], so also a British subject, in whatever land he may be, shall feel confident that the watchful eye and the strong arm of England will protect him from injustice and wrong.”
Boot uses this as a basis to criticise the supposedly weak US response to the detention of its citizens wandering across the borders of Axis of Evil countries in North Korea and Iran (notwithstanding today's surprise visit by Bill Clinton to get the two women in North Korea released).
But is Palmerstonian intervention such a great model? Taking up the cause of British subjects or British vessels (as we will see in the moment) was not a policy that can be taken in isolation. Sometimes it had its liberal-sounding motivations (such as in the anti-Semitism directed against Don Pacifico).
But Palmerston was playing Great Power politics even as he offered high minded rhetoric. In the Don Pacifico case, he was manoeuvering to prevent the Greeks getting too uppity (as he saw it) against the Turks, who he needed to keep the Russians in check. Here's another case --
In October 1856 the Chinese seized the pirate ship Arrow. It had been registered as a British ship two years previously but was owned by a notorious Chinese pirate. The titular captain was British, and the crew was Chinese. It was intercepted in Chinese territorial waters by Chinese coastguards and the Union Flag (sic) was pulled down. The Chinese crew was arrested and the British captain was released. The British Consul at Canton, Harry Parkes, protested against this insult to the flag and demanded an apology. The Chinese Commissioner Ye Mingchen refused and it was discovered that the Arrow's registration as a British vessel expired three weeks before it was seized and therefore had no right to fly the flag or to be exempt from interception under international law. However, in disregard of international conventions, Parkes refused to back down in order to save face and protested that the Chinese did not know it was not a British ship at the time they accosted it. Parkes sent the Royal Navy to bombard Ye's palace and it was duly destroyed, along with a large part of the city and a large loss of life.
This became the flashpoint of the Second Opium War in which the British demands included unfettered access to China's rivers, legalized opium, and privileges in the shipment of indentured workers ("coolies") to the USA. Subjugation, drugs, and exploitation. "Liberal interventionism" indeed. If Somali pirates sprung the Stars and Stripes on a ship and another country's navy pulled it down, would that be a cause for war?
But back, as so many British Prime Ministerships do, to the Irish Question. Palmerston had complex views on Ireland (not least because of family links) but part of his outlook saw the northeastern USA (and by extension, the US government) as under heavy Irish nationalist influence. This was one reason for his flirtation with supporting the Confederacy and the rant above about the risks to Canada from the American branch of hardline Irish nationalism.
So what's our point? Palmerston was a product of his time. To go quote-plucking as Boot does is not very helpful. If America is to pursue gunboat diplomacy on behalf of any citizen, anywhere, it's important to know the precedents for such behaviour.