By Ian Johnston LONDON — It is the nation that once ran the largest empire the world has ever known, a country so powerful that it claimed to "rule the waves" in a patriotic anthem.

But last month a "political tsunami" struck the United Kingdom and this once-mighty state faces being broken up.

An astonishing victory for nationalists in the Scottish parliamentary elections means it is almost certain that a referendum will be held within five years on whether Scotland should leave the U.K. and become an independent country.

The Scottish National Party (SNP) won 69 out of 129 seats in Edinburgh's Holyrood parliament, with about 45 percent of the vote, up by more than 12 percentage points. Their three main rival parties — Labour, the Conservatives and Liberal Democrats — all lost ground.

Polls currently suggest only a third of Scots back independence, but the unionist campaign is in disarray and the nationalists boast a leader who even his opponents admit is a highly skilled political operator.

Alex Salmond, Scotland's first minister and leader of the SNP, is the man plotting the demise of the 304-year-old union of the two countries. He hopes his fellow citizens will heed the message of another tune, "Flower of Scotland," the unofficial national anthem which urges Scots to "rise now and be a nation again."

While the U.K. has been one of America's staunchest allies — often concerned with the state of the so-called "special relationship" between the two countries — an independent Scotland would likely be at odds with the U.S. on many issues.

Story: An all-American Scottish nationalist on why the UK should split

The SNP would rid Scotland of nuclear weapons on moral grounds; it would also take Scotland — which lies in a strategically important position in the North Atlantic — out of NATO. And despite being a significant oil producer, the SNP has already introduced what it describes as "world-beating" climate change legislation with a target to cut carbon emissions by 80 percent by 2050.

'Illegal, immoral conflict'

Moreover, the Iraq War was "an illegal, immoral conflict," Salmond told reporters at the Foreign Press Association in London last month, and something that an independent Scotland would never have become involved in.

Leaving the U.K. would give Scotland the chance to create "a socially just, economically prosperous society," Salmond added, and not be "a country that excels in nuclear weapons and dominating others."

"Being a big country is not a question of size and scale, but of the size of your ideas, the scale of your contribution to humanity," he said.

Speaking to msnbc.com, Salmond dismissed suggestions an independent Scotland might have a poor relationship with the U.S., pointing to the mutual warmth between America and the Republic of Ireland, which is not a NATO member.

"We'd be in exactly the same position as Ireland is at the present moment," he said.

"There's a lot of goodwill towards Scotland from people in America," Salmond added, noting Scots had made a "fairly substantial contribution to the intellectual backbone of the American Revolution."

Scotland and the U.S., he said, had "a positive relationship" and that would improve after independence.

Salmond told reporters that separation from the U.K. was an idea "whose time has come."

'Psychological battle'

Asked about the poll ratings, he admitted there was a "psychological battle" to be won to persuade Scots to vote for change in the face of a "scare-mongering campaign" by unionist parties.

But Salmond said the SNP's victory in the May election showed that Scots were gaining in confidence and had rejected the "mendacious message" that Scotland was "too small and too poor to look after its own affairs."

"It was a political tsunami that occurred in Scotland," he said, days after announcing a referendum on independence would be held within the next five years.

But tsunami warnings can come to nothing.

John Curtice, a professor of politics at Strathclyde University and an expert pollster, said the SNP victory appeared to be partly because of dissatisfaction with the other political parties, particularly left-of-center Labour.

Surveys had consistently showed support for independence at between a quarter and a third of voters, he said.

However, Curtice said Salmond had a "remarkable ability to spin a positive case for his party and his country."

And the unionists, Curtice argued, needed to find "a positive argument for staying in the union," rather than rely on negative campaigning, as well as a leader to sell that message.

"Who is going to lead the campaign? Who is there who has the ability to campaign effectively? It's not entirely obvious," Curtice said. "The SNP starts from behind, but you can see the structural weaknesses of the unionist camp."

One possible candidate, Annabel Goldie, currently leader of the staunchly unionist Scottish Conservative Party, has effectively stepped out of contention, saying after her party came third in the elections that she plans to resign.

She insisted that "overwhelmingly, people do not want independence, whatever Alex Salmond may claim," while admitting he was a "very astute politician" with "a very formidable political presence."

"We are at ease with being part of the U.K.," Goldie said. "It is a relationship that many people acknowledge has served people well, not least in the recent recession and banking crisis."

Traditional goodwill

She feared an independent country might lose some of the traditional goodwill Americans have toward Scotland if it was "constantly trying to make grandstanding gestures on the world stage."

Goldie said it "undoubtedly would be a left-of-center, socialist administration with already well articulated views on issues like nuclear — Trident (nuclear missiles) or nuclear energy — and very strong views on social issues ... all sorts of views which are somewhat alien to the American ethos."

One decision that was entirely alien to U.S. traditions was the early release of Abdel Baset al-Megrahi — the only person convicted in the bombing attack on Pan Am 103 over Lockerbie — on compassionate grounds in 2009, just eight years after he was found guilty of the mass murder of 270 people.

SNP Justice Secretary Kenny MacAskill made the decision after doctors reportedly told him that al-Megrahi, suffering from cancer, likely had three months to live. Nearly two years after his release, al-Megrahi remains alive.

The SNP's stance on NATO is another possible source of friction.

The naval base at Faslane on the west coast of Scotland — home to the U.K.'s nuclear submarine fleet — and the safe harbor at Scapa Flow off the country's northern coast are strategically important locations.

Cold War tracking stations

Scotland is also part of a network of sonar monitoring stations — built during the Cold War to track Russian submarines moving into the North Atlantic — that could become important should the old tensions flare up again.

A senior SNP source admitted there was a difference of opinion within the party about NATO membership, with some members so strongly opposed to nuclear weapons on moral grounds that they did not want to be under NATO's "nuclear umbrella."

Defense commentator Stuart Crawford, who served as a lieutenant colonel in the U.K.'s Royal Tank Regiment and later became the SNP's junior defense spokesman, said senior party figures had long wanted to get rid of the party's "bonkers" opposition to NATO.

Crawford, who has since left the SNP but still supports independence, said the idea of a complete disassociation from nuclear weapons had taken hold among grassroots supporters and the party was "painfully democratic."

He said Scotland might have limited significance to the U.S. now, but suggested a possible scenario that would radically change that.

"In 2030, the expanding power that is China says, 'Can we lease a naval base from you Scotland?" ... We'll pay you billions of dollars for the privilege' — then I suggest Scotland becomes very important to the U.S.," he said.

Crawford compared such a move to the Cuban missile crisis, but added: "China is a friendly country, so what could the objection be?"

'Good for the country's psyche'

Crawford said he doubted Scotland would vote for independence in the planned referendum, but said he expected it would happen within 10 to 20 years.

"I'm an emotional nationalist and I think it would be good for the country's psyche and soul as a whole," he said.

For Alan Roden, an Englishman who covers Scottish politics for the Daily Mail newspaper, that would be a shame.

A photo on his Facebook page shows him wearing a traditional Scottish kilt, but makes clear his passion for English football team York City. Many on either side of the border have similar ties and feelings toward the two countries.

One of his "favorite quotes" listed on Facebook makes his opinion clear, paraphrasing a line from the 1707 Act of Union that "England and Scotland shall forever after be united into one Kingdom."

"People want their MSPs (Members of the Scottish Parliament) to stand up for Scotland, but Scotland within the union," he said, noting the same polls highlighted by Curtice.

However, Roden admitted that "you can never underestimate Alex Salmond," saying he was "incredibly popular" and left other Scottish politicians "in the shade."

"This is a man who at the start of the Holyrood election campaign was significantly trailing the Labour Party in the opinion polls but who turned that round … and ended up with the first majority in the Scottish parliament's history," Roden said.

Partly because of the proportional voting system, previous Scottish administrations have been coalitions or have governed with only a minority of the lawmakers, relying on ad hoc support from other parties.

Echoing other commentators, Roden said the unionists needed to unite and "put forward a positive message about why Scotland and England are better together" as well as find a Scot good enough to stand up to Salmond to lead the campaign.

A claim made by some in the unionist camp is that businesses, people generally and English people in particular would leave if Scotland became independent.

'Scotland is my home'

But Roden plans to stay. "Scotland is my home and I do believe the people of Scotland have a right to choose their own future," he said.

Another foreign-born resident of Scotland with a keen interest in the debate is Dr. Mark Aspinwall, head of politics and international relations at Scotland's Edinburgh University.

A native of Massachusetts, Aspinwall said he was "very neutral" about the idea when talking with students, but had been "sort of opposed to it" because Scotland and England "are so linked economically."

But Aspinwall, who has dual citizenship, showed signs of wavering. "I'm not sure how I would vote to be honest," he said of the referendum.

He told msnbc.com that independence was "conceivable," but rated the chances as "less than 50-50."

Scotland "would certainly have a future as an independent country," he said, comparing it to Norway.

"There's something that is Scottish, there is an identity, a pride, a history that's a bit different," Aspinwall said.

"I love Scotland ... It's clean and fresh, open and green. It has the same topography as northern New England, the same mountains, not the same trees ... it's a great place, friendly people, and Edinburgh is a wonderful city, a really cosmopolitan place. It's great here."

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PS- de très nombreux liens dans l'article original. - BF