It was not due to terrain but to Europe's encastellation. The first two invasions of Poland were devastating because the country's villages lacked stone fortifi

It was not due to terrain but to Europe's encastellation. The first two invasions of Poland were devastating because the country's villages lacked stone fortifications and were instead still based around traditional Slavic wooden forts. This was not the case further West and while the Mongols could conduct siege warfare, being so far afield and having to besiege the vast number of castles that dotted the Western European landscape would have completely reversed their momentum. When the Mongols returned to Poland a third time, in 1287-1288, with an even larger force than before, the invasion completely failed because the country's fortifications had been upgraded. The Mongols suffered significant losses and were turned back. During the first two invasions, Western Europe was significantly better fortified than Poland of 1287, so they would almost certainly have been smashed.