[pugio]

I've always wondered what "illegal" means in this context? Is it designed to just be a pejorative, or something incendiary? When is an invasion "legal"? I can't really think of any case where any kind of recognized body of law (especially one that both constituents would recognize) would impose legality on an invasion, so it seems that people say "illegal" in much the same way that "legal" has become a stand-in in our society for "moral".

Should I read it as "immoral invasion"? Leaving aside whether it is or isn't, at least that framing makes sense, because you can meaningfully debate the morality of an invasion, but I can't understand how you could debate legality (except perhaps within the country's own internal framework of laws, like if a president declared a war without going through the proper legal channels).

[impossiblefork]

An invasion can be legal when authorized by the UNSC due to some crisis or when it's done in self-defence or to defend some other country.

So examples of some illegal invasions: US invasion of Iraq, Russian invasion of Ukraine. Legal invasions (although illegalities were found afterwards, but much of the invasion was legal) are the invasion of Libya, probably the NATO invasion of Serbia depending on what actually happened (there are still some open questions-- it matters why people went in).

Reasons to think the Israeli invasion of Lebanon is illegal are the mass-bulldosing of civilian buildings, destruction of farmland, some opinion articles about Lebanese territory being legitimately Israeli territory and an appropriate target for settlement etc. It shows a plan that is not primarily about self-defence.