Good question. I think the term invade has a more neutral meaning in English than in Chinese. The Allied invasion of Normandy was a very welcome event for most Frenchmen....but we still call it an invasion. The British Invasion of the 1960s was a welcome cultural phenomenon that is fondly remembered in the US. We also use the term invasion in the context of civil wars. Here is a Wikipedia article on the Atlanta Campaign....the article uses the word invaded to describe a military operation, and does not imply that the Confederacy was not part of the United States. An invasion may lead to liberation, reunification, independence, or subjugation. This game does not take a position on what happens after the invasion. It is only intended to explore the mechanics of a military operation.
I hope that helps.