Title: 2004–05 Arsenal F.C. season
Content:  Arsenal ended the previous season as league champions, becoming the first side since Preston North End 115 years earlier to do so undefeated. They completed their historic league campaign with 26 wins, 12 draws and 90 points. By the end of January 2004, Arsenal were still in the hunt for all four trophies, but suffered setbacks in each of the cup competitions; they were unable to retain the FA Cup, losing out to eventual winners Manchester United in the semi-finals and days later were knocked out of the UEFA Champions League by Chelsea in the quarter-finals. They exited the League Cup after a defeat to Middlesbrough in early February.
Title: 2011–12 Arsenal F.C. season
Content:  The 2011–12 season was Arsenal's 20th season in the Premier League, and also marked the club's 125th anniversary. In the Premier League, Arsenal struggled to recover from a poor start to the season. Though they did finish the season in the final qualification berth for the next season's UEFA Champions League. Arsenal's UEFA Champions League campaign once again proved unsuccessful, falling at the first hurdle in the knockout stage, with a 4–0 defeat at Milan ultimately proving fatal. Exiting the FA Cup at the fifth round stage at the hands of Sunderland, and the League Cup in the quarter-finals against Manchester City, the two domestic cups were also out of Arsenal's reach. Arsenal finished the season in third place after winning their last league match 3–2 against West Bromwich Albion on 13 May 2012. It was the first season since the invincibles in 2003–04 which Arsenal finished the top London club in the league, or in which Arsenal finished ahead of Chelsea.
Title: History of Arsenal F.C. (1966–present)
Content:  Little did they know it at the time, but the defeat to Leeds would be Arsenal's last in the League for over a year. 2003–04 was a record-breaking season for Arsenal, as they won the Premiership unbeaten (26 wins, 12 draws, 0 defeats), finishing a clear 11 points ahead of second-place Chelsea. They became only the second team to do so, the first having been Preston North End in 1888–89. Their rivals for the title gained revenge in other competitions – Arsenal were defeated in the Champions League quarter-finals and FA Cup semi-finals by Chelsea and Manchester United, respectively, in successive matches. Faced with the potential 
Title: Arsenal F.C. league record by opponent
Content: The table includes results of matches played by Arsenal (including under the former names of Royal Arsenal and Woolwich Arsenal) in the United League, the Southern District Combination, the London League Premier Division, the Football League and the Premier League. Matches from the abandoned 1939–40 season are excluded, as are the games in the various wartime competitions. ; The name used for each opponent is the name they had when Arsenal most recently played a league match against them. Results against each opponent include results against that club under any former name. For example, results against Birmingham City include matches played against Small Heath (1888–1905) and Birmingham (1905–1945). ; The columns headed "First" and "Last" contain the first and most recent seasons in which Arsenal played league matches against each opponent. ; P = matches played; W = matches won; D = matches drawn; L = matches lost; Win% = percentage of total matches won ; Clubs with this background and symbol in the "Opponent" column are Arsenal's divisional rivals in the current season. ; Clubs with this background and symbol in the "Opponent" column are defunct. 
Title: 1988–89 Arsenal F.C. season
Content:  The 1988–89 season was the 94th in the history of Arsenal Football Club. It began on 1 July 1988 and concluded on 30 June 1989, with competitive matches played between August and May. The club ended its 18-year wait for the league title by winning the Football League First Division championship in the most closely fought title race in the competition's history. Arsenal beat Liverpool 2–0 in the final match of the season to take the title on goals scored, as both clubs shared the same points total and goal difference. During the season Arsenal also enjoyed success in the Football League Centenary Trophy, but exited the League Cup to Liverpool in the third round and fell at the same stage of the FA Cup to West Ham United. 
Title: 2003–04 Arsenal F.C. season
Content:  final game of the league season was against Leicester City. They conceded the opening goal, but turned the match around in the second half through goals from Henry and Vieira. With 26 wins, 12 draws and no defeats, the team became the first since Preston North End in 1888–89 to go through a league season undefeated. Reviewing the match and overall season, Amy Lawrence of The Observer wrote: "Arsenal's achievement may not make them 'great' in everyone's opinion – those who define greatness only by European Cups, back-to-back titles, and triple cartwheels on the way to every goal – but it is staggering in its own right."
Title: Arsenal F.C.
Content:  from 7 May 2003 to 24 October 2004, a national record. Arsenal finished in either first or second place in the league in eight of Wenger's first nine seasons at the club, although on no occasion were they able to retain the title. The club had never progressed beyond the quarter-finals of the Champions League until 2005–06; in that season they became the first club from London in the competition's fifty-year history to reach the final, in which they were beaten 2–1 by Barcelona. In July 2006, they moved into the Emirates Stadium, after 93 years at Highbury. Arsenal reached the final of the 2007 and 2011 League Cups, losing 2–1 to Chelsea and Birmingham 
Title: 2001–02 Arsenal F.C. season
Content:  The 2001–02 season was the 104th season of competitive football played by Arsenal. Having ended the previous season as FA Cup finalists and league runners-up to Manchester United, the club went one better in this campaign, by completing the domestic double – their second in four years and third overall. Arsenal won the Premier League by a seven-point margin, were unbeaten away from home and managed the unique feat of scoring in every league game. They lost only three times in the division, all of which at home. At the Millennium Stadium, Arsenal beat Chelsea 2–0 to win the 2002 FA Cup Final. 
Title: Arsène Wenger
Content:  as he guided his team to an undefeated domestic league season – something achieved only once before in English football, by Preston North End, 115 years previously. Arsenal later eclipsed Nottingham Forest's record of 42 league matches unbeaten and went seven more matches before losing in October 2004. Under him, the club made its first appearance in a Champions League final in 2006, though the team lost to Barcelona. Wenger oversaw Arsenal's relocation to the Emirates Stadium, and prioritised the club's finances in his second decade to meet costs. This coincided with a nine-year spell without winning a trophy, before Wenger guided Arsenal to further FA Cup successes in the 2010s; he holds the record for most wins in the competition 
Title: Arsenal F.C. league record by opponent
Content:  football league system and hold the record for the longest uninterrupted period in the top flight. The club remained in the Football League until 1992, when its First Division was superseded as English football's top level by the newly formed Premier League, of which they were an inaugural member. In 2003–04, Arsenal completed a league season without a single defeat, something achieved only once before in English football, by Preston North End in 1888–89. Arsenal's first team have competed in a number of national, and in the early part of the club's history, regionally contested leagues such as the United League, the Southern District Combination and the London League Premier Division. Their record against each club faced in these 

Question: when did arsenal won the league?
Answer: 2004–05 FA Cup.