In your Seller Admin > Cart Shipping Settings > Shipping Destinations list, you probably have only United States selected.
If you will ship worldwide, just hold down Ctrl (PC) or Command (Mac) and click United States again to deselect it, so nothing is selected in the list (selecting nothing works the same as selecting everything for worldwide shipping).
If you will only ship to certain countries, just hold down Ctrl or Command and select those countries in the list.
Click Next to save changes, then on the next screen you can just click Back to Admin.