General elections in Northern Ireland are dominated by the battle between the forces of unionism and nationalism.

But in addition to that tribal contest, there will be bitter exchanges among rival unionists, and between competing nationalist groups, as they wrestle for supremacy inside their own communities.

And while the arrival of devolved government saw the parties work together more successfully than ever before at Stormont, the novelty of handling bread and butter issues for the first time also gave them a whole new set of issues to fight over.

This election will see the first major foray into Northern Ireland by the Conservative Party through its electoral pact with the Ulster Unionists, but despite the Tory promise to offer a new "non-sectarian" alternative, they too have become mired in the politico/religious divide.

Northern Ireland has 18 Westminster constituencies and at the last election the DUP won nine, Sinn Fein took five, the nationalist SDLP won three and the Ulster Unionists took one seat.

Issues on the agenda include the battle between unionism and republicanism, rival parties' performance in government at Stormont, the scandal over MPs expenses and the continuing threat of violence by dissident groups opposed to the peace process.

The start of 2010 saw political upheavals in Northern Ireland that make this general election one of the most difficult to predict, but the DUP will struggle to avoid losses, Sinn Fein will have difficulty making gains, and the SDLP face a battle holding their South Belfast seat.

The Ulster Unionist pact with the Tories has got off to a rocky start, but they have unveiled a list of candidates that present the possibility of breaking new ground as they stand under the awkwardly worded banner of Ulster Conservative and Unionist New Force.

Each of the main parties, however, faces challenges in this campaign:

The DUP - If the main unionist party had a battle plan for this election, they tore it up in early January

The party leader Peter Robinson was rocked by the headlines over his wife's young lover, and DUP strategists were sent back to the drawing board.

But the DUP faced problems even before that particular earthquake.

The party grassroots, weaned on opposition to all things green, remain unconvinced of the merits of entering government with Sinn Fein.

Ian Paisley led his followers into bed with Martin McGuinness and Gerry Adams, but since he handed the leadership over to Mr Robinson, the East Belfast MP has found it difficult to soothe hard-liners while also keeping his coalition with Sinn Fein afloat.

The scandal over MPs' expenses further irritated voters. Worse still, Mr Robinson and his MP wife Iris were dubbed the Swish Family Robinson when it emerged that they and the relatives they employ took home £571,939.41 a year in various salaries and expenses.

The DUP suffered a hammer blow last June when the European election saw Northern Ireland's new unionist hard men - the Traditional Unionist Voice (TUV) party - seize 13.7% of first preference votes in their first major political outing.

The figure mirrored the scale of the DUP collapse, with its vote plummeting by 13.8%. And to make matters worse, the split in the unionist vote saw Sinn Fein top the poll for the first time.

After the European election, the DUP reverted to talking tough and trying to block or delay republican policies at the Assembly, especially the Sinn Fein demand for the swift transfer of policing and justice powers from Westminster as their price for having agreed to support the reformed police service three years ago.

By January 2010, it seemed republican patience had snapped and they would bring down the government. But it was precisely at that point that the floodgates opened over the DUP.

It emerged that Iris Robinson, one of the DUP's leading figures and wife of its leader, had an affair with a 19-year-old and secured £50,000 from two property developers to fund a business for her lover, but failed to declare it to the authorities.

For a party which traditionally marched with a bible in one hand and a ballot box in the other, it was a scandal of Old Testament proportions.

Amid fears that Sinn Fein could crash the Assembly and force a snap election, the two parties entered protracted negotiations. They emerged agreeing to devolve justice powers within weeks and promising unionists a new system for overseeing loyal order parades.

But with battle lines drawn, the Ulster Unionists are nipping at the DUP's heels and TUV leader Jim Allister is to contest the talisman North Antrim seat held by Ian Paisley. Meanwhile Iris Robinson was forced to step down in her Strangford constituency.

The DUP leadership face a tough election.

Sinn Fein - The republican party was strengthened by the recent signing of the deal on devolving policing and justice powers.

The agreement also promised progress on issues important to republicans, including new government backing for the Irish language.

The deal came just in time for a party that succeeded in drawing the DUP into government in 2007, but failed since then to get it to agree to any policy with even a hint of green in it.

The impression that Sinn Fein hopes were being frustrated at Stormont were followed in recent weeks by events which embroiled its leader in political controversy and personal tragedy.

Gerry Adams faced complaints that he mishandled allegations that his brother Liam abused his daughter. The Sinn Fein President said he will give evidence against his brother on behalf of his niece, but news of Liam Adams' former role in Sinn Fein despite the abuse allegations caused political tensions.

Gerry Adams denied wrongdoing and, amid the controversy, he disclosed that his own father was an abuser.

The West Belfast MP also said his wife Collette was diagnosed with cancer and underwent surgery in recent weeks.

The issues arrived after a period when his party faced pressure over its role at Stormont. But thanks to the recent deal with the DUP, the Sinn Fein leadership can now tell supporters its strategy to deliver change through its role in government is beginning to bear fruit.

Critics hope to capitalise on the party's handling of the education portfolio at the Assembly, and its controversial efforts to end academic selection in schools. The issue will undoubtedly figure on the hustings, but it notably failed to hurt the party in the Euro poll.

Sinn Fein refuses to take seats at Westminster, and Northern Ireland's demographics mean that, without an upset, it's hard to identify how it can add to its tally of MPs.

:: The SDLP - The party's newly appointed leader Margaret Ritchie, who is its sole minister in the Stormont government, has had little time to put her mark on the SDLP but has declared her intention to rebuild the party which has been overtaken by Sinn Fein.

The SDLP has entered a phase of rebuilding, with the introduction of some new faces. It is best known for its historic role in helping to end the Troubles, but is trying to find a fresh identity for the future.

Its new leader has concentrated much of her energy on attacking the DUP, and especially Sinn Fein, over their leadership of the power-sharing government.

The SDLP has a firm grip on its Foyle seat, is the favourite to hold South Down, but could face a battle to hold South Belfast, which unionists are keen to regain.

The Ulster Unionist Party - The UUP has been on a rollercoaster over recent months, but luckily for it, the headline writers have been focused on the Iris Robinson scandal.

For two years it built up its plan to field joint candidates with the Conservative Party in an electoral pact backed by David Cameron.

The partnership promised to be a non-sectarian platform that offered Protestant and Catholic voters a chance to step away from the old "Green and Orange" rows and play a role in the next Government.

The plans were dented by the refusal of the UUP's sole MP Lady Sylvia Hermon to stand under the Tory banner.

But the new era was dealt a hammer blow, when it emerged in January that the Tories facilitated secret talks in Hertfordshire between the UUP and DUP.

Was Mr Cameron lining up DUP support in any future hung parliament? And if he was cuddling up to the two unionist parties, where did this leave his political platform in Northern Ireland and what did it suggest for his future stewardship of the peace process if he ever became prime minister?

Things looked even worse when it emerged that the UUP and DUP also held secret talks with the Orange Order, aimed at devising new tactics to restrict the growth of Sinn Fein.

David Cameron was by then being asked awkward questions about Northern Ireland by interviewers.

The UUP suddenly "clarified" its position, distanced itself from the DUP and tried to draw a veil over the episode.

But if there is a hung parliament, the Conservatives might be less coy about their special interest in the unionist parties.