Ultimately, the reason why love and compassion bring the greatest happiness is simply that our nature cherishes them above all else. The need for love lies at the very foundation of human existence.
When a person is in a miserable situation, then, yes, it is difficult to develop genuine compassion toward others. That's why I find it difficult to say to poor people, "Please have compassion toward millionaires." That's not easy.
In the past, destruction of your neighbour might have been considered a victory, but today we are all interdependent. We live in a global economy; we face problems like climate change that affect us all. The 7 billion human beings alive today belong to one human family. In the context that others' interests are in our interest and our interest is in their interest, the use of force is self-destructive.
Human beings are not intrinsically selfish, which isolates us from others. We are essentially social animals who depend on others to meet our needs. We achieve happiness, prosperity and progress through social interaction. Therefore, having a kind and helpful attitude contributes to our own and others' happiness.
If you develop a pure and sincere motivation, if you are motivated by a wish to help on the basis of kindness, compassion, and respect, then you can carry on any kind of work, in any field, and function more effectively.
Genuine happiness consists in those spiritual qualities of love, compassion, patience, tolerance and forgiveness and so on. For it is these which provide both for our happiness and others happiness.