Global Citizen

What does it really mean to be a global citizen? Sure, don't millions of people interact with each other everyday, not only person to person, but also in cyber space. Sure, wouldn't it be great if everyone understood each other interculturally where ever the place be on this planet. But what about this interculturalism. What about the differences in culture. Anyone can understand, but not everyone can act accordingly.For example, poligamy. Sure they can understand it, but would my parents ever approve if my sister was to marry a man with many wives? What about the war that has raged since the dawn on civilization due to differing religions and culture? Is it possible to become a complete global citizen, without renouncing other global citizens just like your self?