You could rephrase ALL invasions as "defense of another". For example, Putin's excuse to invade Ukraine was 'to "protect the people" of the Russian-controlled breakaway republics.'
Otherwise you're just arguing that countries can point at some random object and say "that's under my watch" and bring armies to fight for that thing. In a sane universe that's called an invasion. Whether the invasion is morally justified or not is another matter.
I'm not talking about stupid mental gymnastics, I'm talking about very straightforward defense against an invasion. Iraq invaded Kuwait, a multinational coalition approved by the UN pushed them out. How is that not defense?
