Interesting note, as of today, the US is the first country to have successful spacecraft missions visit all of the classical planets. There is one big exception, of course: the Soviet Union was the first to have a spacecraft visit Earth, with Spunink. This category is completely arbitrary, especially given that Pluto is now considered a minor planet. Still, it's an achievement of note. Mercury - 1974, Mariner 10 Venu…
I really hope we someday get to the point where no one really cares what "country" achieved the next space exploration milestone.
edit: To be fair, I am really heartened when I see how international the teams that do work in the space station generally are. We've come a long way.