It seems to me that this sentence should be in the imperfect, either because it is an ongoing action in the past or because it is a habitual action. I am definitely struggling with sentences like this, and any guidance is appreciated.
I just thought the exact same thing and would appreciate any info as well
Here, I think the idea in the speaker’s mind is that the invasions were repeated, and constant (i.e. no interruption). And as such the speaker is considering them as a single larger event, akin to having many battles in a single war.