I agree that world government could help solve some problems like climate change. However, there is a risk that it could become a totalitarian world government. In the past, totalitarian governments have not lasted very long because they have been outcompeted by their neighbors. However, if it were a global totalitarian government, there would be no competition, so it could become a permanent state. This is one of the significant existential risks (one that would not let humanity achieve its potential). See the book Global Catastrophic Risks for details.
I agree that world government could help solve some problems like climate change. However, there is a risk that it could become a totalitarian world government. In the past, totalitarian governments have not lasted very long because they have been outcompeted by their neighbors. However, if it were a global totalitarian government, there would be no competition, so it could become a permanent state. This is one of the significant existential risks (one that would not let humanity achieve its potential). See the book Global Catastrophic Risks for details.