As major news events grab international attention, social media has become the new sounding board for the world. And Twitter, with its 320 million monthly users, was the medium favored to quickly spread a story across the globe.
From the horrific terror attacks in Paris to the heartbreaking image of a refugee child's body washed up on a Turkish beach, Twitter was the center of every story - sharing updates, pictures and conveying the emotions.
These were some of the most viewed hashtag topics from 2015.
FILE - LSU students painted their chests with the message "Pray for Paris," the day after the Nov. 13, 2015 terrorist attacks in France.
#PrayForParis
The French capital endured two attacks by Islamist terrorists 10 months apart this year.
In January, an attack on the Paris offices of the satirical magazine Charlie Hebdo killed two police officers and 10 journalists. The hashtag #JeSuisCharlie - French for "I am Charlie" - became a rallying cry in support of freedom of expression. In the days following the attack, #JeSuisCharlie was named one of the most popular hashtags in Twitter history, with more than 5 million uses.
In November, gunmen carried out a series of coordinated attacks in Paris, killing more than 130 people. Once again, Twitter users collectively expressed their sorrow, this time with the hashtag #PrayForParis, which was used more than 7 million times.
FILE - A woman with "Black Lives Matter" written across her cheek attends an ATlanta demonstration against the deaths of unarmed black men at the hands of white police officers.
#BlackLivesMatter
Outrage across the United States over police brutality was raging across social media at the end of 2014. The hashtag #BlackLivesMatter became an avenue of protest both online and in person. #BlackLivesMatter was Tweeted 9 million times this year. The hashtag that started on social media has become a social calling card for activists across the U.S. angry about a string of shootings involving the police and black citizens.
FILE - Two men wearing shirts with "#LoveWins" written on them watch the 2015 San Francisco gay pride parade.
#LoveWins
2015 brought huge victories for the marriage equality movement, with both Ireland and the U.S. legalizing same sex marriage.
After the U.S. Supreme Court extended the right to marry to same sex couples across America in June, people took to social media to celebrate. #LoveWins was used 284,730 times within the first hour after the decision.
U.S. President Barack Obama tweeted his reaction to the ruling using the hashtag. "Today is a big step in our march toward equality. Gay and lesbian couples now have the right to marry, just like anyone else. #LoveWins."
FILE - People take part in a demonstration in support of migrants in front of the Mikolaj Kopernik's statue in Warsaw, Sept. 12, 2015.
#RefugeesWelcome
The wars in the Middle East overflowed into the world in 2015, resulting in the biggest refugee crisis since World War II. As images of boats overladen with refugees began to emerge, smartphones and social media became primary means of communication and connection between the refugees and those trying to help them.
The image of a refugee child washed up on a Turkish beach spurred European citizens to demand their governments open the doors to the displaced. #RefugeesWelcome became one of the top moments on Twitter in 2015.
FILE - A man holds a sign supporting Ahmed Mohamed, who was arrested when teachers and police mistook a clock he built and brought to school for a bomb.
#StandWithAhmed
In September, a 14-year-old Texas schoolboy, Ahmed Mohamed, was arrested after teachers mistook the homemade electronic clock he had brought to school for a bomb.
The hashtag #StandWithAhmed became the rallying cry for global outrage over injustice based on ethnicity and religion. Ahmed saw such widespread support on social media that President Obama invited him to a White House event. He has since moved with his family to Qatar.
FILE - A journalist looks at Vanity Fair's Twitter site with the Tweet about Caitlyn Jenner, the transgender Olympic champion formerly known as Bruce, featured on the July 2015 cover of the magazine.
Celebrities
After Caitlyn Jenner unveiled her transition from former Olympic decathlon winner Bruce Jenner on the cover of Vanity Fair magazine, her Twitter account reached 1 million followers in a little more than four hours.
Followers of the European boy band One Direction accounted for half of the 10 most recirculated tweets, including the three most popular. The number one retweeted message on Twitter was that of One Direction band member Harry Styles, who tweeted "All the love as always. H," after Zayn Malik announced plans to leave the group.