> By that definition, the US invasion began in 2014 too. Who do you think primarily supplied Ukraine with weapons and training?

Im not sure what you think an invasion is, but wouldn't a foreign power, stationing their military in your country without your consent qualify?.

Where as when you invite another military to help you out its not really an invasion?.

No, Russia literally had military presence in Ukraine by 2014, see the occupation of Crimea.