Personally, I don't think this is achievable in the foreseeable future

Maybe some time, generations and generations away when humanity is forced to behave and is taught that conflict only leads to more conflict. But how would that have to be achieved? Most likely some authoritarian figure seizing power and uniting the nations through force. Then, when 'peace' is achieved under this one government, people would start to doubt its authority, there would be a growing disparity between the working class and the upper class, and possibly the government itself would, like all governments, eventually become corrupt. It's simply unachievable this way. So maybe through anarchism? All states are dissolved, no more borders. So here comes the second definition of anarchy. There would be rampant crime, who would be there to stop people from causing crime, your neighbour? They have their own family to worry about. It's unachievable through any mean I can think of.