"If you want to easily defeat the country, start feeding it with your food."
This quote by Ivan the Fourteen means that if, the country you want to defeat, you need to enjoy the victory over someone else's land, thereby recognizing the enemy from the side, so that he is tired to find out what he is capable of and what are the weak spots, and you have to feed them and give them water, so that they do not think and could hardly move, and after eating it is better not to fight.
That's what the quote of Ivan the Fourth means.