Realpolitik is the management of foreign policy decisions by carefully calculating levels of power and and matching the results up against the national self interest.
What does that mean?
It means, that if one state begins to gain in power relative to its neighbors, other states should either increase their own power to balance it, or (and more likely) should band together into alliance(s) to counter the threat.
It is not a matter of whether you like your new allies.
Nebulous abstracts such as humanitarian issues cannot interfere (not that I necessarily disapprove of considering such issues in decision making - that is a discussion for another node). Power, force, threat, and leverage are the issues that you focus on - no more and no less.
In short, reality forces you into making a political decision.
IMO, the British have usually used this well with their Balance of Power philosophy for the European continent. On the other hand, a commonly held academic belief is that realpolitik directly contributed to the conditions that precipitated World War I, from the complex alliances that "naturally" evolved from the rise of a strong, unified Germany. | 
