If we're talking purely about military performance and not about which nation won or lost any given war then the US military wins hands down. I don't think anyone comes close to our kill:loss ratio in the post WWII era.
But as far as I know the only nation to achieve most of its tactical and strategic objectives in the WWII era is Israel. Israel's miltary acheivements are particularly impressive when you consider the geopolitical landscape it has had to deal with since its inception.
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