How are international policies shaped?

Would a country choose their ideology over their interests?  In what scenario would that ever happen?  After the class discussion tonight, it seems to me that the general consensus is such - countries will always choose their interests over their ideas EXCEPT in the case where their interests could possibly start WWIII.  Since no country is interested in actually starting WWIII, they will repress their interests to avoid war.  As one person in class said - "we aren't going to burn down the house with us inside it." 

So here's how I picture it: ideas shape interests which states act upon, then if the international perspective paints the action as being unfavorable, the state will then justify their action with another, more acceptable idea.  I think the only real exception to this is when a state's action puts global interests at risk - that's when international organizations such as the UN step in, world powers take notice and the state's interests have to be repressed for the good of the globe.  Careful negotiations have to take place, but disaster is avoided. 

Another image that came to mind is one of the ideas being the rails that the policy train starts on, then as the train continues down the track and new information is uncovered or different circumstances arise, the train is diverted along different rails so that the policy that the train ends up at is different than the ideologically driven track it started on.  Indeed, in this case, the train starts off with ideas and then ends up being diverted by interests until it ends up at an interest-driven policy.  Some policies are perhaps able to stay on the ideas-driven track, but the cynic in me believes that those are rare instances

Another thought that I wanted to bring up, but couldn't figure out a way to is this: the idea that the only states who can have idea-driven actions are the states whose interests are well in hand or well advanced.  For instance, I remember in a philosophy class the idea was mentioned that ancient civilizations only produced philosophers if their economy was sufficiently advanced to the point where the entire populace didn't have to worry about where their next meal was coming from.  In the same way, countries are not able to really act upon their ideals when they are not stable enough to ensure their interests.  In this way, the US is able to give foreign aid which could be argued to be driven by our ideals (though personally I think it's more likely a great PR stunt on the international stage while perhaps being interest-driven in ideas of future reciprocity) since we are pretty well assured of our interests.  I remain convinced that ideas and interests are so intertwined that we can't really tell where one begins and the other ends, or even if they do.  However, I must say that this topic has been very enjoyable to debate and explore.