There'd be no wars, we don't war with our brothers and sisters, Jews help each other out, they don't kill each other.
Just look at Israel for the most legitimate example, Jews from all parts of the world, all creeds are welcomed with open arms and helped with their new lives in the holy land, this would be the same if everybody in the world were Jewish, simply extended out to encompass the whole world. But it's a funny question, because Jews only want Israel, we don't want the world, the world is for everybody else.