Fusion Tables support geometries that can be defined using the Keyhole Markup Language format. That can fulfil the highlighting requirement. Yet, that would mean defining the geometry of each country visited manually; it requires an effort I’m not prepared to make. Fortunately, it’s possible to "join" multiple tables - it’s called merging. Merging creates a new table, with both tables associated in it. Even better, if any of the initial table data changes, it’s reflected in the merged table.

Good news: there’s an existing publicly accessible table defining all country geographies. Let’s merge the existing table with it in File Merge. In the Or paste a web address here field, paste the URL from the world countries above. Click Next. The opening pop-up requires to define the "join" columns of the tables.

Click Next. In the opening pop-up, tick the checkboxes of columns that will be part of the merged table. Click Merge. Wait for the merge to happen. Click View table.

Now, on the world map tab, changing the Location field to "geometry" yields the expected result.