It had existed as a phrase for some time, but it wasn’t until two black men died in the summer of 2014 that Black Lives Matter began to flicker to life as a Twitter hashtag.

The roots of the phrase are commonly traced to a July 2013 Facebook post by Alicia Garza, a California-based activist, but it appeared in the Twitter-friendly form #BlackLivesMatter only in fits and starts over the course of the following year, according to a Pew Research Center analysis on race and social media released this month.

The hashtag had a small, but sustained increase in use in the summer of 2014, when Michael Brown and Eric Garner died in encounters with the police, focusing a national discussion on race and policing and elevating a phrase that would define a movement.

[Read more on the missing Black Lives Matter activist who was found dead.]

“This is a very powerful example of how a hashtag now is attached to a movement, and a movement, in some ways, has grown around a hashtag — and a series of really painful and really powerful conversations are taking place in a brand-new space,” said Lee Rainie, director of internet, science and technology research at Pew.