The split between CART — which subsequently became Champ Car — and the IRL had begun in 1996 when Indianapolis Motor Speedway president Tony George reserved most of the starting grid at the Indianapolis 500 for IRL competitors, forcing CART's established teams to choose between running IRL equipment or skipping the race. The two series operated in parallel for over a decade, dividing the sport's teams, drivers, sponsors, and broadcasters. CART filed for bankruptcy after the 2003 season, and a group of former CART team owners reorganized it as the Champ Car World Series, which continued through 2007.
By the mid-2000s, the IRL had absorbed most of CART's major teams and manufacturer support. Honda, Toyota, Chip Ganassi Racing, and Team Penske had all moved to the IRL by 2003. Champ Car operated primarily on road and street courses with an increasingly international schedule, including events in Australia and Europe, but lacked the Indianapolis 500 and the television presence that had once defined CART's commercial strength.
Discussions about unification had occurred at various points during the split era, repeatedly failing due to conflicting financial interests and the personal tensions surrounding Tony George's role in the original division. A more concrete push began in late 2007. On January 23, 2008, George offered Champ Car management a proposal that included free cars and engine leases to Champ Car teams willing to run the full 2008 IndyCar Series schedule. In return, the IRL would add Champ Car's contracted dates at Long Beach, Toronto, Edmonton, and Australia to the IndyCar schedule.
The offer required resolving a scheduling conflict: the Indy Japan 300 at Twin Ring Motegi was slated for the same weekend as the Grand Prix of Long Beach, a flagship Champ Car event. On February 10, 2008, George, along with IRL officials Terry Angstadt and Brian Barnhart and former Honda executive Robert Clarke, traveled to Japan to discuss moving the Japanese race. The meetings were described as optimistic.
In February 2008, George and the owners of the Champ Car World Series completed an agreement to unify the sport for the 2008 season. Champ Car was suspended with the exception of the Long Beach Grand Prix, which ran as a standalone event under Champ Car branding to fulfill its contractual obligations before being absorbed into the IndyCar calendar. The IRL purchased substantially all of Champ Car's assets, and most former Champ Car teams joined the IndyCar Series using equipment provided by or sourced through the IRL.
The unified series officially recognized the championship records and race histories of both CART and the IRL, integrating them into a single historical ledger for American open-wheel racing.
Randy Bernard was named the new IRL chief executive in February 2010. In 2011, the sanctioning body officially dropped the Indy Racing League name and adopted IndyCar to reflect the merged and broadened character of the series. The new Dallara DW12 chassis was introduced for the 2012 season, replacing the Dallara IR-05 that had been the IRL's spec car.
The reunified series reflected the structure CART had built at its peak. Former CART stalwarts Chip Ganassi Racing and Team Penske returned to prominence as frequent race winners. The grid included a substantial contingent of foreign-born drivers. The schedule evolved to include more road and street courses than oval tracks, reversing the oval-only founding philosophy of the IRL. Hybrid powertrains were later added beginning with the 2025 season.
The reunification ended the competitive war between the series but did not immediately restore open-wheel racing to the standing it had held before 1996. Attendance at the Indianapolis 500 continued to decline for several years after reunification, with the race not selling out again until 2016. The combined series never regained the manufacturer competitiveness, sponsor base, or television ratings that CART had commanded in the early 1990s at its commercial peak.
Many analysts concluded that the split had inflicted structural damage on American open-wheel racing from which full recovery was uncertain. The NASCAR Cup Series had firmly established itself as the dominant form of American motorsport during the split era, and that position proved durable even after open-wheel racing resolved its internal governance crisis. The reunification nonetheless gave the IndyCar Series a stable platform from which to rebuild, and the combined series has maintained consistent competition and international race wins through the subsequent decades.