WILLIAM BRANGHAM: New Zealand has long been known for its progressive policies, including efforts to correct and address historical wrongs against its indigenous Maori population.

But, as Ali Rogin reports, a new right-wing government has reversed many of those policies and triggered mass protests in the Pacific nation.

ALI ROGIN: They marched for nine days in the dark and through the rain, carrying portraits of generations past and the flag symbolizing their right to self-determination.

Protesters from New Zealand's native Maori community walked alongside non-indigenous New Zealanders to form what's thought to be the largest March in the nation's history.

The peaceful show of force culminated last month in the capital, Wellington, outside Parliament.

At the protest's heart, a bill proposing changes to New Zealand's founding document, the Treaty of Waitangi, or Te Tiriti o Waitangi.

MAN: To safeguard, to honor, to protect Te Tiriti o Waitangi.

WOMAN: Why are we doing this?

Why are we bringing a bill in where there is already a foundational document in there?

ALI ROGIN: Signed in 1840, the treaty helped establish New Zealand's first colonial government and promised land and other rights to Maori.

CARWYN JONES, Lecturer, Te Wananga o Raukawa: The Treaty of Waitangi is certainly seen as being part of our Constitution.

ALI ROGIN: Dr. Carwyn Jones, a Maori legal expert, says, for more than a century, the government mostly ignored the native rights set out in the treaty, pushing many Maori off their ancestral lands and into poverty.

ANNOUNCER: The column now seems to number an excess of 4,000 people.

ALI ROGIN: But decades of activism has led to increased treaty recognition in New Zealand law and policy.

Today, the treaty is interpreted as a partnership between the government and its native people, who make up almost one-fifth of the country's population.

CARWYN JONES: What that meant in terms of the courts is that government has an obligation to act as a treaty partner, to act with utmost good faith and reasonably towards the other treaty partner, with Maori.

ALI ROGIN: That's led to legal acknowledgment of some Maori rights such as land rights, services that address Maori socioeconomic disadvantage, and official status for the Maori language.

CHRISTOPHER LUXON, Prime Minister of New Zealand: I mean, let's be clear.

There's a strong depth of emotion on all sides of this debate.

ALI ROGIN: That progress, many believe, is threatened by last year's election of the most conservative government New Zealand has seen in a generation, a coalition of three parties led by former airline executive Christopher Luxon.

CARWYN JONES: It is one of the most anti-Maori governments we have seen in a long time.

And this is the first government in a long time which is deliberately rolling back on those rights and taking us backwards in that respect.

ALI ROGIN: In the last year, the government has shut down an agency that addressed Maori health disparities, made it difficult for local governments to have dedicated Maori representation, and scaled back the use of the Maori language by government departments, but most controversially: MAN: Christopher Luxon, you are presiding over the most racist piece of legislation in 100 years.

ALI ROGIN: ... it helped introduce a bill into Parliament that would fundamentally change how the treaty is interpreted.

DAVID SEYMOUR, New Zealand Minister for Regulation: Well, my bill would replace those principles of so-called partnership that have been invented by the courts over the last 50 years and say, no, no, no, for the most part, people would have equal rights before the law in New Zealand.

ALI ROGIN: David Seymour, who himself has Maori ancestry, leads the right-wing backed party and is the architect of the legislation that would effectively remove some Maori rights recognized in the treaty.

DAVID SEYMOUR: This bill, as a matter of fact, takes nothing away from anybody, unless you're one of those people who believe that you should have special rights over and above others as a consequence of your birth and your ancestry.

And we just reject that.

ALI ROGIN: The reaction was loud, swift, and viral... (CHANTING) ALI ROGIN: ... when some Maori lawmakers, led by the country's youngest member of Parliament, Hana-Rawhiti Maipi-Clarke, launched into a haka, a ceremonial dance, in protest.

KASSIE HARTENDORP, Director, ActionStation: When we saw her do that, we were all immensely proud and knew she was doing the exact right thing on behalf of all of us.

ALI ROGIN: Kassie Hartendorp is a Maori activist who helped organize the largest petition against the bill and attended the protests outside Parliament.

KASSIE HARTENDORP: Get people signing up to make submissions against the Treaty Principles Bill.

ALI ROGIN: She says removing unique Maori rights ignores the historic disadvantages her community has experienced.

KASSIE HARTENDORP: We die younger.

We're more likely to be locked up in prison.

We have every negative health statistic you can imagine.

And so we do not live equal lives.

We have not been afforded equality.

So to now be told that our sovereignty is standing in the way of supposed equality is just a lie.

ALI ROGIN: In a recent poll, more New Zealanders said they opposed the bill than supported it, but most said they don't know enough about it.

Many legal experts, including at New Zealand's Ministry of Justice, say the law could throw the country into a constitutional crisis.

CARWYN JONES: It would effectively be the end of the treaty relationship.

If you undermine that relationship, then you start to take away the legitimacy of government.

You start to erode social cohesion if you are not willing to give effect to a recognized Maori right or to act in partnership with Maori.

ALI ROGIN: Prime Minister Luxon has said he only promised to support the bill through the first stage of review and that his party will not vote for its passage.

CHRISTOPHER LUXON: Treaty issues are complex.

They have been negotiated, debated, discussed over 184 years.

It's simplistic to assume that you can, through the stroke of a pen, resolve all of that.

ALI ROGIN: While this law is likely doomed, after a year of rollbacks of Maori rights, many fear what will come next.

KASSIE HARTENDORP: Our current coalition government is stripping back indigenous rights on a whole raft of laws.

My concern for the future is that a far right populist movement will grow in nature to be able to strip us of the sovereignty that we were guaranteed to those 200 years ago.

Therefore, we need to make sure that we keep this up and make sure that they stick to their word into the future.

ALI ROGIN: An ongoing battle over New Zealand's past in order to define its future.

For the "PBS News Hour," I'm Ali Rogin.