"We have chosen this day, the 250-year anniversary of the British Royal Proclamation," Clayton Thomas-Muller, one of the leaders of the Idle No More movement, said in a statement.
"We are using this founding document of this country and its anniversary to usher in a new era of reconciliation of Canada's shameful colonial history, to turn around centuries of neglect and abuse of our sacred and diverse nations."
The 1763 proclamation set rules for European settlement in North America, recognized First Nations' land rights and laid out the groundwork for the treaty process.
Idle No More organizers said more than 50 events were taking place in Canada, the U.S. and in other countries. One of the largest was at the B.C. legislature over proposed pipeline projects to which First Nations communities have been lining up in opposition.
In Victoria, 250 people gathered outside the legislature to show their support in the fight against climate change and what they described as Canada's plans to expand the energy industry at the expense of the climate.
Protesters carried a long, black pipeline mock-up that stretched across the building's front steps, the slogan "Pipelines, Gateway to Climate Disaster" written across the side. Others toted placards that read, "B.C., Not a Carbon Corridor."
Eugene Boulanger, 26, from the Northwest Territories, said Canada's politicians need to know that Canadians of all stripes are concerned about climate change and the impact of resource development on First Nations rights.
"I wish our elected leadership in this country could use their imaginations and that they could provide us with other options besides tar sands and pipelines," Boulanger said.
Meanwhile, Prime Minister Stephen Harper, NDP Leader Tom Mulcair, Liberal Leader Justin Trudeau and Gov. Gen. David Johnston all released statements about significance of the proclamation.
In Ottawa, the head of Canada's largest aboriginal group said the anniversary should be the catalyst for action on a number of fronts.
"Two-hundred and fifty years, we still, with every government — including this one — are saying that the time for First Nations to help drive a future must be led by them," said Shawn Atleo, national chief of the Assembly of First Nations.
"Not just on land. On education, in child welfare, in all aspects of our lives. So it is an important moment. What's even more important than the words that we're hearing, including the words that go back to the 2008 apology, (is) it's time for action."
Among other issues that need to be addressed, Atleo said, is an inquiry into the hundreds of aboriginal women who have been murdered or who have gone missing.
The governing Conservatives have so far not heeded calls for such an inquiry. Atleo said Aboriginal Affairs Minister Bernard Valcourt has not given him any indication that the Conservatives would commit to a public hearing.
"He's not mentioned it, but I remain hopeful," Atleo said. "Our people remain resolute."
Atleo added that he hopes the visit to Canada of a special United Nations fact-finder will draw worldwide attention to these and other issues.
The UN has dispatched American law professor James Anaya to speak to First Nations representatives and government officials as he drafts a report for the world body. He arrived in Canada on Sunday evening and will travel the country before leaving next week.
Later Monday, during a visit with Valcourt to an Ottawa school, Atleo underscored the significance of the Royal Proclamation.
"Hundreds of treaties were made because of the Royal Proclamation," he said. "And I would say maybe Canada wouldn't exist without the Royal Proclamation."
— With files from Dirk Meissner in Victoria.
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