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I completed the map on the 3rd attempt. This time, I started with the territories of Russia (Moscow). The main challenge of the map, as mentioned above, is the appearance of aggressive enemies while you are not yet fully developed. In previous attempts, and this time as well, I had to retreat from the starting lands, leaving only 1-2 "native" castles, develop in other territories, and then gradually reclaim them, depending on the strength of the enemy.
In the last playthrough, there were 2 such strong enemies. After unsuccessful battles, I simply avoided clashes with both and went to conquer distant lands, and only later, at the end, did I deal with one and prepare for the second, but I couldn't find him; apparently, he disappeared in a battle with the first one.
Overall, the map is large, and you should try to complete it at least once for the experience.