In order to answer this question, it is important to know the difference between a simple sentence and a compound sentence. A simple sentence is defined as a sentence that has one clause, containing a single subject and a predicate. An example of a simple sentence is, “I ran to the store.” The sentence has a single subject (I) and a single predicate (ran to the store).
Another example of a simple sentence is “Jessica jumped and cheered at the game.” You might think that this is a compound sentence because it contains two verbs (jumped and cheered), but it is still a simple sentence that contains a compound verb.
In order to combine “United we stand. Divided we fall” into a simple sentence, we must first create a single subject (“we”). Then, we can move to combining the verbs. One answer to your question is “We stand united but fall divided.”