Invasions are by definition hostile. Mexico could move into a near-majority Hispanic border state like CA or NM, say it is moving in to protect Hispanics from gringo violence and disarm Federal troops and local police without firing a shot. No one would dispute that this was a hostile act against the US.
Hitler's annexation of the Sudetenland was accomplished not only without any violence - it was done so with the express approval of the Allied Powers. When the war was over, most Germans were expelled from Czechoslovakia, with the exception of those who had proved their loyalty, via acts of resistance against the Third Reich. Crimeans who side with Russia had better be sure the Russians will win. If the Ukrainians get it back, the Crimeans most prominent in siding with the Russians will face the fate of the Tories who sided with Britain against the Patriots during the American Revolution - expulsion.
If Mexico had military bases hosted in the autonomous region within our borders where the Mexican immigrants live, and that region came under threat due to a revolt in D.C. that forced Obama out of office, then yes, I would say they too have a reason to saunter in peacefully to show they’re willing to protect their people if need be.