Our differences :)
What is holding humans back from working together on a global scale?
Egos.
Common goals.
Religions
Greed
Language barriers
Governmental philosophies
Hate.
Politics.. The big game that only the entitled play
Racism. Things may be getting better but they are far from being good.
materialism.
Arrogance
There is a saying that "man dominates man to his harm". When cooperation is needed for a common goal people who have more resources, influence, etc often take the lead and the team effort is lost. People have trouble working together without hurting each other, compeiting, being dishonrst, selfish, etc. This is a global issue that causes much critical times.
Religion, Government, Military, and Money.
These things were never nesasary on this place.
Egos and Envy. From these, the rest is born.
We are at certain levels. The International Space Station for example. You can go on GitHub and there are millions of people all over world collaborating and working on projects together.
What's holding us back? Education. Pure and simple.