Its the highest contributor in terms of obese people in numbers for sure
Sure but you can't ignore a 20% obesity rate all throughout Europe just because the US is worse.
The gene pool is pretty much identical (at least for whites, which is a fairly large sample of the US population anyway) in Europe and in the US so the massive increase of obesity in the US is certainly due to specific factors that are specific to the US in terms of lifestyle or food products.
there are a LOT of countries all over the world with obesity problems, US is just high up the list, but we are very much not alone. So let's stop blaming the US for everything, OK?