BBC Northern Ireland
The 2010 Westminster election will be Northern Ireland's 20th full election since 1987.
In that time Northern Ireland has seen a polarisation of the vote on all sides, and, in more recent years, a deepening split within unionism.
That tendency to split was emphasised by the appearance last year of Traditional Unionist Voice (TUV) at the European Election, while the nationalist vote has been consistently divided between the Sinn Fein and the SDLP.
As the charts below show, the biggest changes in unionism since 1987 have been the reversal in fortunes of the Ulster Unionist Party (UUP) and latterly the Democratic Unionist Party (DUP), as well as a "squeezing out" of smaller loyalist/unionist parties.
In the wake of the Anglo-Irish Agreement, unionists were temporarily united in their opposition to any form of Irish government involvement in Northern Ireland.
In a demonstration of broad community support for this position, the UUP remained the largest party, despite losing their South Down seat to the SDLP. The DUP retained their three seats - East Belfast, North Antrim and Mid Ulster.
As the British and Irish governments continued to review the security situation into the 1990s, it became clear that a new approach of negotiation and engagement with the IRA was needed if any progress was to be made.
An IRA ceasefire in 1994 paved the way for secret talks between Sinn Fein leader Gerry Adams, SDLP leader John Hume, and the British Government.
In May 1996, elections to a Northern Ireland Forum for all-party talks were held.
This coincided with a resumption of violence by the IRA, followed shortly afterwards by another ceasefire.
The DUP emphasised their rise in popularity over this period by becoming the second largest party elected, with 24 seats, just six behind the UUP's 30.
In May 1997, as Tony Blair swept into power in Britain in an historic election victory for "New Labour", the political landscape in Northern Ireland became more fractious.
The DUP made a 7 point gain in their share of the unionist vote, whilst Sinn Fein's popularity increased on the nationalist/republican side.
The DUP ended up losing a seat - Mid Ulster, to Sinn Fein's Martin McGuinness. The UUP retained their 10 seats.
After years of talks, the Good Friday Agreement was signed in the spring of 1998.
The Agreement was broadly supported by nationalists and republicans, and was endorsed by the UUP. The DUP refused to support a deal giving Sinn Fein a place in government while the IRA still hadn't decommissioned its weapons.
A substantial minority of unionists - 43% - voted "no" in the Agreement referendum, endorsing the DUP position.
At the Assembly elections, the DUP earned 20 seats, just 8 behind the UUP.
The SDLP were on 24 seats, Sinn Fein on 18.
Also included in the new Assembly were the UDP and PUP, loyalist-affiliated parties, both pro-agreement.
However, both quickly lost ground; by 2007 only Dawn Purvis, of the PUP, remained as an MLA.
Amid division in the UUP, the DUP gained steadily in the polls, jumping another 15% in the unionist vote in 2001.
After the Assembly suspension in 2002, in the wake of the IRA spy-ring allegations at Stormont, the DUP finally overtook the UUP in the 2003 Assembly Elections.
Sinn Fein surpassed the SDLP as the largest nationalist party. Jeffrey Donaldson, Arlene Foster and Norah Beare all resigned from the UUP and joined the DUP in December 2003.
The 2005 General Election was a disaster for the UUP: leader David Trimble lost his seat in Upper Bann to the DUP's David Simpson, and the SDLP won the South Belfast seat, capitalising on the split unionist vote.
The UUP were left with one seat, with the DUP on 9, the SDLP on 3 and Sinn Fein on 5.
In July 2005, the IRA announced that they had begun decommissioning, a task completed by September.
Pressure was on the DUP to commit to negotiation on devolution and power-sharing.
With little progress being made, the British Government tried to initiate all-party talks.
The negotiations resulted in the St Andrew's Agreement: Sinn Fein were committed to full acceptance of the new Police Service of Northern Ireland, the DUP to power sharing with republicans and nationalists, and both sides to the full devolution of policing and justice powers within two years.
As part of the deal, Assembly elections were held and the DUP won 36 seats, twice that of the UUP, Sinn Fein won 28 and the SDLP just 16. The Executive was restored in May.
The same year, Jim Allister, DUP MEP for Northern Ireland, resigned from the party in protest at the decision to share power with Sinn Fein.
In the European Election of June 2009, Mr Allister lost his seat but his new party, Traditional Unionist Voice, took more than 66,000 first preference unionist votes.
He had made a significant impact, taking most of his votes from disillusioned DUP voters.
When the Hillsborough Agreement was forged in February 2010, paving the way for full devolution of policing and justice powers to Northern Ireland,
Mr Allister repeatedly voiced his opposition to the deal.
The DUP eventually united in favour of devolving policing powers but the view of DUP voters on the move is yet to become clear.