This is a complete sentence. There are a few ways to tell if a sentence is a fragment or if it’s complete. One of the best ways to tell if something is a sentence fragment is to see if it makes sense on its own. It will typically denote a full, complete thought. If it starts with “when”, “where”, “how”, etc. or “and”, “because”, “or”, etc., it’s typically a fragment. These don’t express a complete thought unless the fragment is added to another sentence or the word is taken away.
Since this sentence makes sense on its own and doesn’t start with the phrases I have mentioned, it is a full thought. It’s a complete sentence. It’s also historically accurate.