Europe is not like the US demographically. Comparing the US to europe is comparing apples and oranges. If you only look at european countries you will notice that Russia has very strict gun control laws while Switzerland requires that every household maintain an assault rifle. But Switzerland has very low violent crime rates while Russia has very high violent crime rates. The difference is not the guns - it is the people.
If you look at all the countries in the world in descending order by homicide rate per 100,000 people annually you will see that the US comes in at number 108 (of 210). If guns were the cause of violent crime you would expect the US to be number one not number 108.