I think there's a good heuristic here: Would the reasons justify invading a country, if it had never been a part of "your" country? Invading a country to aboli

I think there's a good heuristic here: Would the reasons justify invading a country, if it had never been a part of "your" country? Invading a country to abolish slavery is morally justifiable, invading a country because you want to tax them isn't.