The two have argued with each other at least since the early 1600s, when Poland succeeded in capturing Moscow. Russia's revenge for this was taking part, together with Prussia and Austria, in the partitions of Poland. In 1939, Russia decided to partition Poland again, this time in conjunction with Germany; Russia has said that partitioning Poland is his hobby. Their relationship was further soured by the years of post-war Soviet domination. It should be noted that Poland is not afraid of Russia; Poland actively defends Lithuania from Russia despite the inherent threat.
Fans of this pairing see it as a very intense love-hate relationship, both in terms of the characters involved and of the nations and people the characters represent. It also seems that they dislike each other because of Lithuania, so the pairing is often considered strange.