Which country's disappearance would impact the world the most?

This may not be news but is definitely a current affair so here goes:

I was born in Portugal and it looks to me that it wouldn't make any difference to the world were the place to just slide down to the Atlantic abyss. Chuck Spain in for good measure and how much would that upset global geo-politics? Or Britain, were the island to sink under the immigrant hordes and what would the rest of the world change about their ways the next day?

Saudi's disappearance would cause a massive spike in oil prices, Israel's would have a serious impact perhaps even in terms of preventing future strife, Russia and China would be big casualties but... so what if China vaporized? Somebody else would replace them as a cheap source of goods, it wouldn't cause any significant upheaval on the borders let alone beyond them. NK might fall but it is doomed to one day anyway.

So are the US worthy contenders for top dog on earth? Ridding the world of their financial and military weight in the world stage would cure all evil on earth in the eyes of some but it would, for instance, make it virtually impossible for Corbyn to resist Trident. ISIS' leader would immediately pop outside for some fresh air and get on the mobile to his mates around the world to make sure they know Satan is dead. China might feel tempted to gobble up Taiwan, who would prevent them? Putin could invade whatever he felt like, next morning there could be Russian tanks in the Baltic States, all over Ukraine and what if he invaded Poland, how much of NATO would be left without the US?

Without the US on this earth Israel would be left terribly vulnerable, the price of charlie would collapse, NASA would be a terrible loss for the world, the movie industry would never be the same, the impact on so many areas would be truly global. They are indeed the world's policeman and nobody would be there to replace them as such the next day, that would have more of an impact than that of any other country's striking off the map. Imagine WWII without the US, where would that have gone?

So they are the most influential nation on earth. How much would Britain's disappearance from the map affect the world in a geo-political context?