Now I will deal with the list of countries you gave which have a higher murder rate than the US. One of the criticisms which Oralloy made about lists of countries with lower murder rates than the US is that many are tiny, and you can't compare these really small nations to a huge, dynamic country like the US. I agree. Also, since the US has a GDP per capita of 55,000, we should be compared to countries with GDPs per capita in that range. There is a chart where countries in brown and very dark red are over $32,000, so we will use that chart. Countries below that line are likely to have a greater percentage of people whose backs are financially to the wall which will usually drive up murder rates.
Here's the chart:
So now, here's your list of countries:
Lithuania and Estonia: Too small, (pop 3 Million and 1.3 Million respectively), and not quite wealthy enough.
Argentina: Not wealthy, GDP per capita = $13,428
Montenegro: Too small and too poor
Uruguay: Too small, (pop 3 Million), too poor, GDP per capita = $16K
Russia: Big, diverse, but poor. GDP per capita = $9,000. Compared to US' $55,000.
Seychelles: Too small, pop under 100,00
Bermuda: Too small, pop under 100,000
A look at the large, diverse, wealthy countries like Germany, UK, France, etc all yield murder rates about one fourth of the US murder rate. These places don't have super lax gun laws like the US.