Why was Poland so important that Russia repeatedly invaded it in the past?
Poland was Russia’s prime strategic rival to the West long before Germany and the US
Ever since we in Russia decided that “Moscow is the third Rome, with no room for the fourth”, Poland had effectively been the only Slav country with the capacity and ambition to challenge us for the role of unifying power for all Slavic peoples of Europe
Poland was the prime conduit of Western cultural imports to Russia up to Peter the Great and his opening of Russian trade routes in the Baltic Sea. Russian has as many loan words from Polish (and German/Jewish through Polish) as from Turkic languages
In terms of geography, if you plan a land invasion to Russia, your way is through Poland. If you are Russian and want to conquer Europe, you must take Poland first. The Carpathian mountains to the south and Baltic Sea to the north leave you no room for maneuver,
The favorite Polish ideas of constitutions, noisy parliaments, aristocratic liberties and powerless monarchs have always deeply offended our Russian sense of popular justice, spiritual destiny and Großrussisches Reich (“Великая Русская держава”)
They are Catholics, we are Orthodox, and we find repulsive their habit of clothing face-shaved priests in sissy white and letting people sit during the services