Except that in 1996 there were just north of 130M guns in the US and a murder rate of 7.4. In 2014 there were 310M guns and the homicide rate was 4.5, a rate not seen since the 1950s. More guns simply do not correlate with more violent crime and, as we all know, a lack of correlation does -disprove- causality.

As for your comparison with "other countries," the US is actually quite low worldwide. There are a small group of countries we are usually compared to due to superficial economic similarities but, when you look at actual population, geography, demographics and cultural history, those countries are not particularly sound comparisons.