To enable an International Shipping option click on Selling > Prices, Shipping, Tax > Shipping
In the upper right corner click on Add or Remove Shipping Options put a check in the box for International and change the label in the box if you wish to then click Save.
On the Shipping page click on Edit next to your shipping option and price the International box with the price you wish to charge your clients for international shipping.
Note: When enabled, this option is automatically selected for orders with a shipping address outside of the country associated with your account.
Disabling this option DOES NOT disable the ability for your international customers to place their orders; it simply removes the shipping option from being displayed during checkout. (Your international clients can still check out using any of your other shipping options.)
Similar to the other options, this shipping option can be renamed to anything that you'd like. The most common name is simply "International Shipping."