Many people would argue that the International Space Station is one of the most extraordinary human accomplishments in space exploration. Considering the short-lived space stations of the pre-ISS era, it really is an astonishing achievement. The thing is, it needed a lot of people to get it off the ground (pun definitely intended).
To quote Wikipedia:
The ISS programme is a joint project among five participating space agencies: NASA, Roscosmos, JAXA, ESA, and CSA.
Now, as in the past, we are looking far beyond Earth orbit, primarily to Mars (although President Obama has the Moon back on the table). However, whenever I hear the phrase "men/women on Mars", it is always in the context of an American mission by NASA. Such a mission seems pretty hard for one nation alone. Doable? Yes. After all, we did put men on the Moon (but that was during the Cold War). But it would still be very difficult. So my question boils down to this: Are future large-scale manned missions (e.g. Mars and beyond) likely to be international efforts, or just from one country? Why?