Four-times winner Italy failed to qualify for the World Cup for the first time in six decades after losing the playoff to Sweden 1-0 on aggregate.
Despite three quarters of possession, Italy were frustrated by a goalless draw in the second leg at San Siro on Monday.
"It's a black moment for our game," Italy midfielder Daniele De Rossi said. "Unfortunately, there will be a lot of time to analyse it. The only thing I can say is that we showed few ideas and not much in the way of tactics."
Sweden advanced to their first World Cup finals since 2006.
It could have been worse for Italy, as Sweden were denied what looked like two clear-cut penalties for handballs, first by Matteo Darmian and then Andrea Barzagli.
Italy had a penalty appeal of its own waved off by referee Antonio Mateu Lahoz when Marco Parolo was tripped from behind by Ludwig Augsustinsson.
But the Azzurri struggled to carve out clear chances against a solid Sweden side, and of their six shots on target, only one really tested goalkeeper Robin Olsen.
"We all need to look within and find a way to bounce back," defender Giorgio Chiellini said. "We need to get back to the level we deserve to be at."
This will be the second World Cup missed by Italy. The first was in 1958.
The last major competitions Italy failed to qualify for were the 1984 and 1992 European Championships.
It would be easy to lay the blame squarely on Gian Piero Ventura. The Italy coach will naturally take the lion's share, but the Azzurri's problems run much deeper.
The rot started long before Ventura took charge.
After winning the World Cup in 2006 for a fourth time, Italy went out at the group stage of the next two editions. They fared somewhat better at the European Championship, reaching the final in 2012 and going out in the quarter finals in 2008 and 2016.
However, Antonio Conte's Italy side overachieved in France last year, when they beat Spain in the round of 16 before losing on penalties to world champions Germany.
For a long time, Italy has lacked a creative force, successors to Andrea Pirlo and Francesco Totti of the 2006 side who could change a match with one moment of magic.
Mario Balotelli was the star of Euro 2012 but fell out of favour after Italy's woeful showing at the last World Cup.
The lack of stars in the Italy team is reflected in the Italian league.
Juventus have been a force to be reckoned with in recent years in Europe, where they have reached two out of the past three Champions League finals. But while their defence forms the backbone of the Italy team, its midfield and attack are made up mainly of overseas players.
The Brazilian-born Jorginho was handed his competitive debut by Ventura, and the midfielder impressed with some deft passing. Jorginho created Italy's best opportunities with two throughballs for Ciro Immobile, who hit the netting from a tight angle from one. Immbobile beat Olsen with another but Andreas Granqvist got back for a goal-line clearance.
Alessandro Florenzi was also back following a year out after twice tearing a knee ligament, and the midfielder forced Olsen into his only real save, while a cross of his was also deflected onto the crossbar in the second half.
Meanwhile, the highly-rated Lorenzo Insigne played only 15 minutes of the playoff, and out of position.
Those three players are 26 or under and, along with forwards Immobile and Andrea Belotti, could form the spine of a rejuvenated Italy side for years to come.
Italy will have to go forward without captain and goalkeeper Gianluigi Buffon, who has played his last international match after 20 years between the sticks for the Azzurri. De Rossi also announced he was retiring after the playoff, as did defender Andrea Barzagli.
Remarkably, the 0-0 result was the sixth straight in the playoffs, since Sweden's goal at home against Italy on Friday.