Full coverage: 50 Dead in Orlando Nightclub Shooting

Most of the mass shooting rampages in the United States have been carried out by gunmen with legally-obtained guns. According to the Washington Post, the US has over 300 million privately-owned guns, almost the same with the country's population of about 300 million too. Meanwhile, the Gun Violence Archive said last year alone, about 50 thousand cases of gun-related violence happened in the US, leading to the death of 13 thousand people.

Prior to Sunday's attacked, the deadliest recent mass shooting in the U-S was from 2007. Then, a Korean student who killed 32 people on the Virginia Tech campus, before eventually killing himself. There've been others.

Columbine High School, 1999 - two teens killed 12 students and a teacher, before taking their own lives.

In 2012, in Connecticut - 20 children and six adults were killed at Sandy Hook Elementary.

Last year, a white supremacist shoot and killed 9 people at an African-American church bible study. The list goes on and on.

In the past, mass shootings quickly led to a debate about gun laws, which vary from state to state. In his remarks, President Obama didn't specifically call for tougher gun policies. But criticize how easy it can be for some to get weapons, and told Americans "we have to decide if that's the kind of country we want to be".