How does Northern Ireland's power-sharing government work?

Sinn Féin has emerged as the biggest party in the Northern Ireland Assembly, after last week's elections.

However, the party's vice-president, Michelle O'Neill, cannot become first minister unless the Democratic Unionist Party (DUP) - which had been the largest party since 2007 but has now been pushed into second place - nominates for the position of deputy first minister.

This is because of Northern Ireland's power-sharing system of government, which was introduced in the 1990s as a way of ending decades of violence.

The principle of power sharing is what sets Northern Ireland apart from the UK's other nations.

It means that in any government there must be representatives from both the nationalist community - who favour unity with the Republic of Ireland - and unionists, who want Northern Ireland to remain part of the UK.

The idea is that, whatever their historic differences, both communities have a vested interest in the system.

A chamber of 90 members (MLAs) is elected to the assembly at least once every five years.

Five MLAs are elected in each of the 18 constituencies using a system called single transferable vote (STV), which ranks candidates by preference.

Northern Ireland has a first minister and a deputy first minister - one unionist, the other nationalist.

Since 2006 the first minister has been chosen by the largest party in the assembly. If this is a unionist party, then the deputy minister is drawn from the largest nationalist party, and vice versa.

Both ministers have equal powers, and one cannot be in office without the other. If either the first minister or the deputy first minister resigns, the other is also forced to resign, whether they want to or not.

The executive, or cabinet is multi-party, and ministers are drawn from both unionist, nationalist and non-aligned parties, based on how many seats they have won in an election. This also means that politicians from smaller parties can be appointed as ministers.

The assembly exercises powers over matters including the economy, education, health, and more recently, Covid.

Certain areas - including international relations and defence - remain reserved for the UK government in London.

Northern Ireland was created in 1921 and remained part of the UK, when the rest of Ireland became an independent state.

This created a split in the population between the unionists - who were mainly Protestant - and nationalists, who were predominantly Catholic.

From the late 1960s, armed groups from both sides, such as the Irish Republican Army (IRA) and Ulster Defence Association (UDA), carried out out bombings and shootings.

This period was known as the Troubles - it lasted almost 30 years, and cost the lives of more than 3,500 people.

Peace talks started in the early 1990s, culminating in the signing of the Good Friday Agreement in 1998, which ended the worst of the violence.

It was endorsed in a referendum with 71% voting in favour. Under its terms, Northern Ireland found itself run by a new power-sharing assembly.

The assembly has endured but it has also been suspended a number of times. The longest suspension was between 2002 and 2007, during which time Northern Ireland was run once more from London.

Relations between the two main parties broke down again in 2017, and the assembly and ruling executive were not restored until January 2020.

In February this year the DUP's Paul Givan resigned as first minister, in protest against the Northern Ireland Protocol.

This is the section of the UK's Brexit deal with the EU which keeps Northern Ireland aligned with the European single market, and protects the movement of goods across the border with the Irish Republic.

However, it also involves creating border controls between Northern Ireland and the rest of the UK.

While most of the politicians elected to the assembly are in favour of the protocol remaining in place, unionists are not happy at what they perceive as a weakening of Northern Ireland's bond with Great Britain. The issue has caused street protests and unrest in some areas.

Now that Sinn Féin has become the largest party in the Assembly, its deputy leader, Michelle O'Neill, stands to become first minister.

While DUP leader, Sir Jeffrey Donaldson, said that his party would respect the election result, his party says it won't nominate any ministers to an executive until its concerns about the protocol are addressed by the UK government.

And on Thursday, the party said Sir Jeffrey would not be taking up his Assembly seat in Lagan Valley, instead choosing to remain an MP until issues with the the protocol were resolved. Former MLA and MP Emma Little-Pengelly was co-opted to his seat at Stormont.

Sinn Féin has accused DUP leader Sir Jeffrey Donaldson of holding society to ransom by threatening to paralyse the Assembly.

The foreign secretary, Liz Truss, has said the UK will have "no choice but to act" if the EU does not show flexibility over the protocol, but it's unlikely any movement will happen before the Northern Ireland Assembly sits on Friday.

If no agreement is reached on the protocol and the DUP do not nominate a deputy first minister, other executive ministers who held office before the election - such as the health minister and education minister - can stay in post for up to six months.

If a solution cannot be found after that time, there would either need to be further negotiations or a fresh election.

The DUP has also refused to say if it will support the election of a new Speaker to the assembly.

If it does not the assembly cannot function, MLAs cannot hold debates in the chamber or scrutinise ministers.