WHEN the last Rugby World Cup drew to an end, with New Zealand having seen off their old rivals Australia at Twickenham, the Six Nations was in danger of becoming a second-tier competition.

Not a single Northern Hemisphere side made the semi-finals four years ago. England, despite being hosts, were embarrassed at the group stage. France shipped more than 60 points to the All Blacks. A supposedly progressive Ireland were thrashed by more than 20 points by Argentina.

It felt as though world rugby’s balance of power had tilted irrevocably towards the nations located south of the equator, but as the next World Cup draws near, the landscape has shifted once more. Instead of being an irrelevance, the Six Nations Championship that begins with Wales’ trip to Paris tonight looks like being a key indicator to who will triumph in Japan this autumn. Indeed, given how closely matched the sides are, it could be harder to win the Six Nations than the World Cup itself.

Ireland boss Joe Schmidt has certainly been adopting that attitude, insisting that the World Cup could not be further from his thoughts as he completes his side’s preparations for tomorrow’s tournament opener against England in Dublin. That is probably over-egging it, but you can understand Schmidt’s reluctance to look too far into the future.

After years of playing the underdog card, Ireland suddenly find themselves having to handle the pressure of being reigning Six Nations champions and strong tournament favourites. And for all their recent success, retaining the Six Nations trophy is devilishly difficult, let alone the even holier grail of claiming back-to-back Grand Slams.

France were the last team to win successive Grand Slams, and they only had to beat four opponents to achieve the feat in the late 1990s. There have only been five back-to-back champions this century, but Ireland could easily make that six if they maintain the form that has earned them two victories over the All Blacks in the last two years as well as their Six Nations success. Ireland are the team New Zealand fear most ahead of the autumn – the next couple of months could easily show why.

Irish rugby is in the middle of a golden age, with the Test side’s run of 18 wins from their last 19 matches having been accompanied by a string of impressive performances from the Irish provinces in the Pro14 and Champions Cup.

Ireland’s set-pieces are the envy of pretty much every other side in the world, and the strength in depth in the Irish game means Schmidt has world-class options in every position. In-form second row Tadhg Beirne misses tomorrow’s game through injury, but the presence of Iain Henderson, Devin Toner and James Ryan means he will not be missed.

Ireland have to play three of their five fixtures away from the Aviva Stadium, but it is hard to see them slipping up in Rome or Edinburgh. Facing Wales in Cardiff on the final weekend could be a different matter – especially if the game is a title decider – but provided Ireland get off to a winning start, they could be extremely hard to stop.

Will England be able to trouble them tomorrow? Eddie Jones’ side were impossible to predict in the autumn – running the All Blacks close one week, almost crashing to a humiliating defeat to Japan the next. They appear to be heading in the right direction, but if the World Cup is starting to look like it might come a bit too soon for them, it is hard to see how the Six Nations will see them at their peak.

That said, however, they will still pack a punch, with tomorrow’s game in Dublin set to be a heavyweight meeting in every sense of the word. When England feel vulnerable, they tend to revert to type, and Jones has assembled a formidable pack featuring a fit-again Billy Vunipola and a back-to-form Maro Itoje.

The make-up of the backline remains a work in progress, but Owen Farrell will feel he has a point to prove following his return to his favoured position of fly-half and Manu Tuilagi will certainly be out to make an impression as he makes his first Six Nations start since 2013. If England can start with a win tomorrow, the tournament will open up for them, with home games to come against France, Italy and Scotland. Their recent record in Dublin, though, suggests that is a very big ‘if’.

Perhaps Ireland’s biggest threat will come from Wales? There’s a sizeable ‘if’ involved with them too, but if Warren Gatland’s side can win in Paris tonight, they should mount a viable title challenge.

Wales’ successful autumn moved them up to third in the world rankings, and they finished second in last year’s Six Nations, running Ireland close before eventually succumbing in Dublin. They have home advantage against the Irish this time, but need to start strongly to ensure they are still in the mix come the final weekend.

The loss of Taulupe Faletau is a blow – the number eight is nursing a broken arm – and having lost the services of the recently-retired Sam Warburton, Wales are also without Rhys Webb, who cannot be selected following his move to Toulon. They are three big absentees, but Gatland has turned the Welsh into a well-oiled side in the last 12 months. They have to be considered title contenders.

Scotland probably can’t finish as champions, but they’re more than capable of ruffling anyone’s feathers, especially at Murrayfield. Their home game with Ireland on the second weekend should provide a strong indication of where their World Cup hopes currently lie, but while their backline will cause problems for whoever it is up against, with Stuart Hogg once again set to be one of the stars of the tournament, the absence of John Barclay and Hamish Watson could diminish their ability to compete at the breakdown.

France? They’ll once again be France, capable of putting 40 points on Wales before shipping 40 points at Twickenham next weekend. England will be especially keen to monitor their progress as they will be group opponents at the World Cup, and while autumn’s defeat to Fiji was an embarrassment, the French are finally starting to show signs of cohesion.

Italy, as ever, will bring up the rear, with their home game against France likely to provide their best chance of claiming a victory.