Terrorist invasion of Ukraine

Bohuslav Sobotka jumped on the bandwagon yesterday and called the presence of Russian troops in Ukraine an "invasion." Use of this word raises a number of prickly questions. How many boots on the ground are required to constitute an invasion? A thousand? Three hundred? Were the U.S. special ops that went into Syria also an invading force? (The Guardian said Yes.) And if the pro-Russian separatists in eastern Ukraine are terrorists, as Petro Poroshenko insists, are the 1,000 unofficial Russian troops now in Ukraine also terrorists? Should diplomatic relations with Russia be suspended, on the grounds that we do not negotiate with terrorists (as Miloš Zeman has stated repeatedly)? Furthermore, can Nato now use the argument posited in the case of Syria and cross into Russia, because Putin ignored the Ukrainian border first? Instead of speaking of an invasion or of terrorists, maybe it would be better to stick to calling the Ukrainian situation a civil conflict, or even a civil war, in which each side is getting on-the-ground help from its allies.