#BlackLivesMatter (BLM) are an international human rights activist organisation that was founded in 2013 in response to Trayvon Martin's murder. Their mission is to eradicate white supremacy and campaign against institutionalised violence and systemic racism in order to create a space in society for 'Black joy'.
Why saying 'All Lives Matter' is problematic
The phrase 'All Lives Matter' sprang up in response to the movement during 2013 and commonly continues to be used as an immediate reaction to the phrase today.
Saying 'Black Lives Matter' is not a confrontation, it does not mean that black lives matter more than other lives. It is ,however, important to highlight the value of black lives within a society where ethnic minorities are disadvantaged and discriminated against. People who say 'All Lives Matter',even despite good intentions, are often accused of degrading minority experiences and the phrase acting as a form racial gaslighting (a psychologically recognised form of emotional manipulation) in which Black people are lead to question their perception of personal suffering.