Unification of the human race is making the human race like one. This can mean, as it were, anything. However, there is e.g. unity of knowledge—such as if every able enough adult were to learn a type of math-problem solving, then it might be said that the human race were to have been united. That's a fact that those who are able to perform a type of math problem solving are united — in knowledge. This is an exampli gratia. Most commonly people are said to be united in political preference (e.g. "Democracy") — but mankind never has been — except in that murder is illegal — which we declare is a universal preference. Although mankind has never been perfectly united in most senses, its unification is still a project that has been and is continually pursued, with successes.
Globalism is a kind of unification, as in theoretically the human race being united in one economic grand-zone.
The United Nations are said to have enacted a unification of the human race. There is of course no end to it. There's always another degree of unification possible since differences always exist. A world without difference is impossible. A world with less relative difference is of course possible.