In the early XVII^th century, the French policy towards Italy was essential because conquering peninsula lands was a good opportunity to harm Spain. In this regard, Richelieu understood the importance of Monaco, which was under the Spanish protectorate and at the gates of the Italian province. Furthermore, the new prince intended to shake off the shackles.  The negociations concluded by the Treaty of Péronne in 1641, started from the 1630s. (full text in French)