At least five Dallas police officers were killed and nine wounded July 7, after a peaceful protest over recent police shootings. Here's what we know so far. (Deirdra O'Regan/The Washington Post)

LONDON — Days after America celebrated Independence Day with flags and fireworks, another week of devastating gun violence unraveled. First, 37-year-old Alton Sterling was fatally shot by at least one police officer. Just moments before, Sterling had been selling CDs in front of a convenience store. About 48 hours later, on Wednesday night, 32-year-old Philando Castile was shot multiple times and killed during a traffic stop. His girlfriend streamed his death live on Facebook while her young daughter sat terrified in the back seat.

"All Americans should be deeply troubled" by the two shootings, President Obama said on Thursday. But only hours later, at least one gunman killed five police officers in Dallas during a protest rally. It was the deadliest day for U.S. law enforcement since the Sept. 11, 2001, attacks, according to the National Law Enforcement Officers Memorial Fund, which monitors the police deaths.

Obama, speaking from Warsaw early Friday, called the Dallas killings “senseless” and pledged that “justice will be done.” He also spoke generally about reforming gun laws.

This week's violence has revived long-simmering debates over gun control, race relations and the use of deadly force by police. Thursday's ambush, at a Black Lives Matter rally to protest the police shootings in Minnesota and Louisiana, put the focus squarely on the intersection of race and gun violence. An attacker told authorities that “he was upset about the recent police shootings” and “wanted to kill white people, especially white officers,” the Dallas police chief said.

Around the world, social media was flooded with people voicing their thoughts and concerns. And once again, many of the posts struggle to understand race relations and gun violence in America.

https://twitter.com/natashananner/status/750970309868683264

The #BlackLivesMatter hashtag began to trend with thousands of people using it both on and offline to campaign against violence toward black people.

Why is the U.S. flooded with firearms?

Those living in countries where most police are unarmed have a hard time understanding how the United States has gotten to this point. From London to Australia, users expressed their thoughts on the Dallas shooting.

"America fights for the right to carry firearms. But when black people carry arms, their life is in immediate danger," reads the tweet below.

"When will the United States understand that firearms are a problem?"

How did the U.S. become a country where mass shootings occur with distressing regularity? 

One Twitter user based in London, where 82 percent of the police said in a 2004 survey that they did not want to be armed, wrote that he was glad to not live in the United States at the moment.

https://twitter.com/YorkshireSlang/status/751321052043673600

Less than a month has passed since the Orlando nightclub shooting, in which 49 victims were killed.

Following the attack, "Daily Show" host Trevor Noah said on air: "The president — he made a powerful point. America has to decide if this is the kind of country that it wants to be. Every time this happens, it feels like America has already decided, this is exactly the kind of country it wants to be.

"Because we know how this always plays out. We’re shocked, we mourn, we change our profile pics and then we move on. It’s become normal. But I’m sorry, maybe it’s because I’m new, but it’s not normal," Noah added.

Last year, almost 1,000 people were killed by police in the United States. This year, there have already been 509 fatalities, according to The Washington Post's police shooting database.

Read more: 

‘Like a little war': Snipers shoot 11 police officers during Dallas protest march, killing five

Minn. governor says race played role in fatal police shooting during traffic stop