With a POD ranging from 1900 to 2020, have foreign troops (a civil war doesn't count) land on American soil (US mainland only, territories like Guam or Puerto Rico don't count, Alaska and Hawaii only count once they gain statehood). This attack can be a ground-based raid, a border clash, or an (partial or full-scale) invasion (sabotage and infiltration operations don't count). You will of course have to make it credible (military power, tactics, logistics, goal and extent of the attack, diplomacy...).
EDIT : Of course, it doesn't have to go full Red Dawn, it can be just, for example, Cuban special forces raiding Key West.
EDIT : Of course, it doesn't have to go full Red Dawn, it can be just, for example, Cuban special forces raiding Key West.