The violence began just over a week ago, when Iraqi security forces disbursed a protest camp in Falluja and arrested a politician who had been friendly to the protestors' goals. This camp was part of a non-violent protest movement – which took place mostly in Sunni cities, but was also receiving some support from the Shia community – that began a year ago. Iraqi security forces have attacked protestors in Falluja and other Sunni cities on several occasions, the most egregious example taking place in Hawija, when over 50 protestors were killed.
...
The Iraqi government's recent actions in Falluja turned the non-violent movement violent. When the protest camp in Falluja was cleared, many of the protestors picked up arms and began fighting to expel the state security forces from their city. It was local, tribal people – people not affiliated with transnational jihadist movements – who have taken the lead in this fight against the Iraqi government.