Nicely done, but the wording sounds odd - if someone asked you "How did America become so strong," you would not say "Liberal," you would say "Liberalism" or some such.
I think the idea of celebrating the liberal ideas that have moved this country forward (and that we're supposedly trying to encourage elsewhere) is a good one, and overdue. Liberals just need to figure out how to separate that message from all of the baggage that has come to be associated with the word: welfare, high taxes, decadence, permissiveness, weakness, elitism, Hollywood, identity politics, etc. They need to give liberalism a new face. Unfortunately, many of them still have trouble recognizing this, and have trouble understanding why so many people respond to the Republican message. But this little movie has the right idea.