What is your story of American government?
You might start with a topic sentence that answers the question. Examples could include: American government is a story of: [pick one] freedom; oppression; immigration; economic prosperity; exploitation; technology or some other concept.
You would then provide several examples of whatever concept you chose. The examples could include Constitutional amendments that extend democracy. Tell the story of each of those amendments. You might focus on examples of racial oppression, the delay in extending the vote to African Americans and to women. You would move from a concept or an idea to categories of events and people that illustrate the concept, then present specific examples that would fall within each of those categories