When was the last time you heard of a non -aggressive campaign? (Um, don't say "presidential," because those get pretty aggro.)

The word "campaign" itself suggests a planned-out takeover: campaigns don't just happen, they're meticulously thought-out stress-fests where trouncing the opponent is the #1 goal. They're inherently aggressive.

Going right along with demonizing communism, Congress uses the line "campaign of aggression" (3) to make it seem as though North Vietnam (and thus communism) is on the march, taking over nation after nation, crushing everything in their path like Godzilla.

Congress uses the words "deliberate" (3) to imply that the aggression is on purpose (no accidental conquests here); and "systematic" (3) to point out that the attacks are targeted and not random.

This type of motif is important to this kind of legal document because it adds a sense of reason and patriotism to the actions that Congress is carrying out. When a country (especially a—gasp!—communist country) is not only campaigning, but campaigning with aggression, you know things are going to get rough.