Ma'ayan Rosenzweig/ABC News

The faces of those 20 first graders massacred at Sandy Hook Elementary School, their devoted teachers and the gunman's mother have made the issue of gun control the subject of an impassioned national conversation, leaving many asking why there are so many mass shootings in the United States.

There are an estimated 88.8 civilian guns per 100 people in the United States, according to the Small Arms Survey, a number unparalleled to the rest of the world. With the right to bear arms written into the Constitution of the United States and the fabric of American culture, it's no surprise that this number is higher than it is in other G-8 countries for which there is data.

But the United States also has a much higher rate of homicides by gun - 3.2 homicides by firearm per 100,000 people, according to the United Nations Office on Drugs and Crime Homicide Statistics.

Even Italy, the G-8 member with the second highest rate of homicides by firearm, comes in far behind the United States. According to United Nations data, a person is 4.5 times more likely to die from gun violence in the United States than Italy.

In France and the United Kingdom, the homicide by firearm rate is 0.1 per 100,000 people. That's one in a million.

The rash of mass shootings, sad occurrences that have become all too common in the United States, have left the country "with some hard questions," President Barack Obama told the grieving Newtown, Conn., community Sunday evening.

"We can't tolerate this anymore," he told mourners. "These tragedies must end. And to end them we must change."