You can specify one Shipping Service as the default service for all International orders. (International orders are defined as having a shipping address with a country code different than the country code set up in your account settings)
Go to Settings > Carriers
Click on the Carrier you wish to use as your Default Shipping Service for International to open the settings.
Select the checkbox for the Default Shipping Service for International
Scroll to the bottom of the page and click Save.
This checkbox overrides any Carrier Mapping for International orders and assigns them to this Shipping Service automatically.
