Join into a simple sentence: United we stand. Divided we fall.
We stand united and fall divided. This remains a simple sentence because it has only one subject, we. The subject has two verbs, but the one subject keeps it a simple sentence. These kind of exercises are good for students to work on in groups as they can argue and explain the difference between phrases and clauses. I used to put my advanced 8th graders into small groups, give them strips of words, and ask them to create two different sentences justifying which was the better sentence. Doing this taught them that parts of sentences are movable which helped them create variety in their sentences. This exercise looks like it would be good for 12th graders especially each group's explanation to the class.