A better comparrison is homicides using a gun per capita.
And whilst it is true that the US doesn't have the highest homicide (using a gun) rate per capitia in the world, it has the highest rate per capitia amongest the develeoped world.
So if we use one of the stats posted above about gun deaths. UK 8, US 10 728 now as the UK population is roughly a fifth of the US comparring them directly is meaningless you have to muliple or divide one by 5 to get a more accurate comparrison accounting for population. So that would be around 40 vs 10 728 when population is factored in.
The UK has very tight guns laws, the US doesn't. Conclusion tight gun laws lead to few homicides by guns.
As for other factors, the same video games/ movies etc.. are available in the UK as the US. Yet the homicide rate is no where near a fifth of the US homicide rate. So the effects of these would appear to be minimal.