Media playback is unsupported on your device Media caption A history of Justin Trudeau saying sorry

Canadian Prime Minister Justin Trudeau has so far issued four formal apologies for historic injustice since his government's election in 2015, beating all his predecessors in government mea culpas. Why is Trudeau Canada's most apologetic leader?

Just over six months after his election, Justin Trudeau stood in Canada's Parliament to say sorry.

His apology was made before descendents of passengers of the Komagata Maru, who were present for the statement.

The Japanese vessel was carrying 376 Sikh, Muslim, and Hindu passengers who were denied entry into Canada in 1914 under immigration laws at the time.

Trudeau called the incident "a stain on Canada's past".

It was the first in a series of formal apologies made by Trudeau's Liberal government to acknowledge historic injustices in the country's past.

Image copyright Courtesu Library and Archives Canada Image caption Immigrants on board the Komagata Maru in 1914

His government is expected to issue at least one more mea culpa, having hinted at recognition of a 1939 incident where Canada turned away Jews seeking asylum from Nazi persecution.

Acting on a recommendation from Canada's Truth and Reconciliation Commission, last year Trudeau also asked Pope Francis to apologise for the Catholic Church's role in the residential school system, where indigenous children were abused for decades.

The pontiff recently turned down the request, saying that while he supported the church's role in reconciliation, he felt he could not personally respond.

Trudeau's propensity for apologies comes in stark contrast to his late father.

Pierre Trudeau, who served twice as Canadian PM, rebuffed calls from the opposition in 1984 to issue a government apology for the internment of Japanese-Canadians during the World War Two.

The elder Trudeau rejected the idea that a government's purpose could be to right the past.

"It is our purpose to be just in our time," he told the House of Commons.

So why is Justin Trudeau so ready to say sorry?

He acknowledged the "different perspective" between father and son at a conference in Toronto late last year.

"(My father) came at it as an academic, as a constitutionalist," he said.

"I come at it as a teacher, as someone who's worked a lot in communities."

He added that "apologies for things past are important to make sure that we actually understand and know and share and don't repeat those mistakes".

Image copyright Reuters Image caption Addressing Canada's parliament, Mr Trudeau absolved the Tsilhqot'in leaders of any wrongdoing.

Canada is, of course, not alone in issuing apologies for past injustices.

Political Scientist Rhoda Howard-Hassmann of Wilfrid Laurier University says one of the earliest notable government expressions of regret came on 7 December, 1970, when German Chancellor Willy Brandt fell to his knees before the monument to the Warsaw Ghetto uprising of 1943.

"That was a highly symbolic act," she says.

Other important formal mea culpas include US President Ronald Reagan's apology in 1988 to Japanese-Americans interned in the camps during the World War Two.

In 2009, there was the UK's posthumous apology to mathematician Alan Turing, who was persecuted for being gay.

In 2011, the Queen offered her "sincere thoughts and deep sympathy" to the victims of Ireland and the UK's troubled past.

In 2015, Pope Francis offered a sweeping apology to "the native peoples of America" for the "grave sins" committed against them "in the name of God".

Howard-Hassmann says political apologies "really started trending in the last 15 years, to the point that some people think it's just getting ridiculous".

"But it is important. "

And many factors go into crafting an appropriate formal apology.

"Formality, ritual, proper venue, proper vocabulary, sincerity, a promise not to repeat [the wrongs], and in many cases compensation - financial or material or symbolic," she says.

Image copyright Getty Images Image caption German Chancellor Willy Brandt falls to his knees before the monument to the Warsaw Ghetto uprising of 1943

Even beyond his formal mea culpas, the PM has not shied away from addressing shortcomings in Canada's collective past.

Trudeau told the UN General Assembly last autumn that "Canada remains a work in progress," citing among other issues ongoing struggles among the country's indigenous communities.

"We can't build strong relationships if we refuse to have conversations," he said.

Historian Jordan Stanger-Ross of the University of Victoria says there can be "a fair amount of skepticism" around formal political apologies.

Be it an attempt to close the book on the past wrongs or the political considerations of key constituencies, "government always has clearly mixed motives in apologising," he says.

The events Trudeau has chosen to apologise for fall squarely in line with the Liberal government's contemporary policies.

The party campaigned on the idea that "diversity is a source of strength" - a stance he referenced in his Komagata Maru speech.

He has been outspoken on LGBT rights.

Image copyright EPA Image caption Canadian Prime Minister Justin Trudeau speaks at the UN general assembly

And Trudeau took power in 2015 promising to fix the country's relationship with indigenous peoples.

His apologies to residential school survivors and the exoneration of six hanged indigenous chiefs underscore that commitment.

Howard-Hassmann says the subject of formal apologies have a few things in common: they are usually backed by a strong social push, there tend to be clear acts of wrongdoing by a specific perpetrator over a specific period of time, and clear victims.

Formal recognition of wrongs are also increasingly linked to financial settlements - in part because we live in more apologetic times.

Fifty years ago "apologies would not have been part of legal agreements", she says.

"You wouldn't be asking for an apology - it would have been seen as symbolic or superfluous."

Both Canada's LGBT "purge" and the Newfoundland residential school apologies included settlements for class actions brought against the government by survivors.

Stanger-Ross says that those settlement funds can add weight to an official apology when money is set aside for the memorialisation of the events.

He gives the example of a British Columbia museum focused on Japanese-Canadian history and culture, created out of apology redress settlement funds, which continues to research the community's story.

Image copyright Reuters Image caption Canada's Prime Minister Justin Trudeau is an advocate for LGBT rights

For individuals who do receive an official apology for past wrongs, the public recognition can be powerful step towards reconciliation.

Simon Thwaites, released from the military because he was gay, told the BBC last June that the LGBT apology "reaffirms the fact that we're not broken, there's not something horribly wrong with us".

Chief Joe Alphonse of the Tsilhqot'in nation in British Columbia, told the BBC this week that Trudeau's apology for the 1864 hanging of five Tsilhqot'in chiefs made for "a very emotional day".

"One-hundred and fifty-four years it took us to get here - 154 years is huge," he said.

But not everyone welcomes them.

In the Canadian Jewish News, writer Sally Zercher said she didn't want the expected apology for the 1939 MS St Louis incident, when Canada turned away a boat full of Jews seeking asylum.

"It will not bring back my relatives, or offer me any solace," she writes.

"Instead, it will whitewash a government that did nothing to help the Jews who were fleeing the Nazis and ignored the type of anti-Semitism that was endemic in Canada until the 1970s."

Mo Dhaliwal, writing in the Huffington Post, argued against Trudeau's first formal apology because "we potentially lose the ability to make the point that the Komagata Maru continues to be as relevant today as it was in 1914".