The easiest, least bloody way to conquer another nation and culture is to COLONIZE IT WITH YOUR OWN PEOPLE AND CULTURE BEFORE YOU INVADE IT WITH YOUR TROOPS.
Our unenlightened, so called "ignorant" ancestors all knew this and were VERY careful who and how many people of other distinctly different cultures, religions, political leanings they allowed to live among them. It has to be people who WANT to embrace YOUR social system or they will make trouble and/or overwhelm and impose THEIR ways upon YOU. "Melting pots" of differing peoples DON'T WORK when no actual assimilation or "melting" is taking place.
Amos Chapter 8: verses 11-13:-11 “The time is surely coming,” says the Lord God, “when I will send a famine on the land—not a famine of bread or water, but of hearing the words of the Lord. 12 Men will wander everywhere from sea to sea, seeking the word of the Lord, searching, running here and going there, but will not find it. 13 Beautiful girls and fine young men alike will grow faint and weary, thirsting for the word of God.