It is not, after all, beyond the realms of possibility that countries will change their foreign policies with the passing of time. Especially in the West, where governments change periodically, one can't really expect their policies to be consistant - one administration might take a directly opposed stand on an issue simply to spite the previous one.

Just one small example is the oft-quoted (especially in the current presidential elections campaigns) so-called "historic bond" between the USA and Israel - as Geez points out above, Israel was affiliated with the other side at the time just after its establishment, and the Americans frowned on that to such a degree that they refused to supply the IDF with the necessary military equipment in the '73 war (the Yom Kippur War), and were in fact only persuaded to mount a last minute air convoy when the very existance of the only democracy in the Middle East was under serious threat.