History

Weird to exclude Luxembourg from that as they were also occupied by Germany and freed by the Allied forces

Edit: checked the book and:

• Netherlands, The: it counts the Battle of the Sluys and other various navel battles fought on Dutch territory as valid examples
• Belgium: it counts the battles that were fought on the land that is now Belgium, so not counting from its creation. It also counts assisting the local people, so for example fighting off the French in defense together with the Flemish

So the book is taking "invasion" more lenient than the comment section:

• The act of invading, especially the entrance of an armed force into a territory to conquer.

The introduction also states "invasion, had some control over, or fought conflicts in the territory"