Conversation so far:
What sort of achievements did the Archduke Charles, Duke of Teschen have?
Despite being epileptic, Archduke Charles, Duke of Teschen achieved respect as a commander and as a reformer of the Austrian army. He was considered one of Napoleon's more formidable opponents.
How long did the Archduke Charles, Duke of Teschen reign?
Archduke Charles, Duke of Teschen reigned from 1792 to 1809.

Question: How did he become Duke?
Self-contained rewrite: How did the Archduke Charles, Duke of Teschen become Duke?