History doesn't necessarily need to repeat itself, and the Portugese analogy might not even be relevant in the first place. Actually, I suspect that major manned space exploration will absolutely need to be a multi-national effort, because of the difficult logistics alone. (Also, a private enterprise/government collaboration). Humanity will need to pool its resources. A Mars trip for instance, would make much more sense as a US/Russian collaboration - think of those Energia boosters ..

One thing you're spot on about: US Robotic exploration of Mars and the outer planets gives us a great deal to be pleased and proud about. (And I'm not even from the US, but from a great lump of land mass to the left of New Zealand).