Context:

So I recently played this old 2007/2009 RTS game called World in Conflict-Soviet Assault, where the USSR decides to invade the the West to prevent itself from collapsing. It's a good game I would recommend(despite a few historical inaccuracies), telling both sides of the conflict in great terms without any bias. So anyways the main point is the USSR has decided to invade the USA through Seattle, Washington through the use of cargo ships disguised as civilian. They are quickly advancing to a (fictional) fort where they may find out that SDI/Star wars project was a failure, which means the USA is NOT invulnerable in the face of nuclear assault(like they believe). To prevent this, the USA launches a tactical Nuclear Missile to prevent any Soviet advance sacrificing a small village and an entire tank company. My question is, can a country do that irl? Can they destroy an invading army on their own land with tactical nukes? Would this be considered a nuclear attack against the invading country?

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Edit: Typo in the title. Its "an", not "and"