Love is the most powerful force in the universe.
I might have a weird definition of love though: love means caring intrinsically about something, rather than caring about it to support some other goal.
So when you say “I love you” you are saying “I care about you and want good things to happen to you regardless of whether it gives me any benefit.”
“If you love someone set them free”. If you just like someone in that you enjoy their company you’ll want to keep them around even if that’s not what’s best for them. If you love them you’ll let them go do what’s best for them even if that’s bad for you.
So what do we love? The most basic love is self-love: who do most people care about the most and most want good things to happen to? Themselves, duh. Beyond that there’s a lot of talk about the love people feel for their spouses, their children, close friends, other relatives, etc. And beyond that you can also love things like your school, your country, or even all humanity in that you care about what happens to people in those categories beyond the effect it will have on yourself and whoever else you love.
Loving only or primarily yourself is called selfishness. Selfish people only care about themselves, not their spouses or families or countries or whatever.
I really don’t encounter that many selfish people. Most people do have some additional love to give. Even bad men love their mamas. What do you call someone who really loves themself and their immediate family, but nobody else? Not exactly selfish, but seems pretty similar if you’re not in the in-group. On the other hand if you are part of that in-group someone with that attitude seems pretty great: they’re prioritizing benefiting you over almost anything else in the world.
This is what racism, nationalism, and such are about: selfishness on behalf of your race or nation or religion or whatever. Who do you love, and who don’t you love? Who are you willing to sacrifice, and on whose behalf? We will do a lot for those we love, and hurt those we don’t not so much because we don’t like them but because they don’t even enter into our calculations.