"One family, one country, one world"...
Those words together like that sound familiar, and not good familiar. Many times has it been attempted in the past, to bring about such a future. Many times, each certainly involving folks who shared that dream of a united world, and each time a complete failure.
Rome.
Holy Roman Empire.
British Empire.
Napoleonic France.
Nazi Germany.
And surely many others throughout the world and history.
Now, it's the United States' turn to try bringing about such a future, and it seems set on failing just like all who tried before.
Humans are socially tribal. That's just how we are as a species. Depending on the school of thought, the human brain is hypothesized to be only capable of comprehending roughly between 150 to 300 individuals, with full knowledge of each person's intricacies and how they relate to everyone else. Past that magic number, which will certainly vary from person to person, we are biologically limited to some form of stereotyping when thinking of other people. That doesn't seem set to change any time soon. It's within THAT framework that we can prevent wars. We can't stop hatred or strife, but we can stop, or at least reduce, war. But it won't happen by trying to force an idealized future onto other people.