Null Sector is an omnic extremist/terrorist group formed in London led by and unnamed Omnic. Their implied goal was to create an omnic nation.
Post Omnic Crisis
20 years ago, a large amount of England was built by omnics working in hard labor conditions. In spite of how much they contributed to society, omnics were treated harshly in the United Kingdom, being denied basic rights and citizenship. Omnics were also treated as though they were criminals or under military occupation, such as being forced through special checkpoints to be scanned, or being marched through streets with armed soldiers close by. Null Sector was formed as a response to this harsh treatment, their goal presumably being to achieve equality between omnics and humans - by force.
Null Sector was supported by local omnic population unhappy with their treatment, and would not hesitate to attack fellow omnics if they were defending the humans. They had great power at their disposal - B73-NS Bastion units, upgraded OR14 units, and more. As time progressed, their control over London increased.
Seven years before the present day, Null Sector launched a surprise attack on King's Row in London, taking the city. The uprising saw London in flames. On the 27th day of the Uprising, the prime minister of the UK expressively forbade Overwatch from interfering. By this point, Null Sector had taken Mayor Nandah, Mondatta, and a hundred other prisoners captive in a guarded power plant and killing hundreds more in the process. Thousands in King's Row needed medical aid. Blackwatch agent McCree reported the hostage situation to Strike Commander Jack Morrison. After much deliberation, Morrison authorized an illegal Overwatch mission to end the crisis On the 28th day of their uprising, the Overwatch agents Mercy, Torbjörn, Reinhardt and Tracer were deployed to King's Row (without the explicit consent of the British prime minister) in order to prevent an attack on the power plant, and put an end to the organization. They fought through many troops, and were ultimately successful in their mission.
7 years after the siege on King's Row, Null Sector has resurfaced and launched a global invasion, strike numerous targeted cities across the planet. The variety of omnics they used there were more advanced and diverse than those from their previous attack.
One of Null Sector's targets was Paris, France, where they began attack en masse. In the midst of the assault, Null Sector was caught off guard by an Overwatch team composed of Winston, Mei and Tracer. Null Sector initially had the tactical advantage in the form of numbers and titan before the fight was joined by Genji, Reinhardt, Brigitte, Echo and Mercy, resulting in Null Sector's contingent being destroyed.