He died when the viscount was but ten years of age, and, his elder brother being but six years older, his mother became regent of the little state.

After having greatly weakened the strength of the Huguenot nobles by the siege and capture of La Rochelle, which had long been the stronghold and bulwark of that religion, Richelieu obtained from the duchess a treaty by which she engaged to remain always attached to the interests of France, while the king undertook to protect the house of Bouillon.

The Duke of Savoy was next compelled to hand over to France the town and province of Pignerol, and Richelieu then turned his attention to Lorraine.

The reigning duke had entered into an alliance with Austria, and the invasion of his territory was therefore the first step by which France entered into the terrible struggle known as the Thirty Years' War.
The duke had given Richelieu an excuse for hostilities.

He had married his cousin, the nearest heir to the dukedom, but he treated her so badly that she fled to France and begged the protection of Louis XIII.