The Relief of Genoa took place between 28 March 1625 and 24 April 1625, during the Thirty Years' War. It was a major naval expedition launched by Spain against the French-occupied Republic of Genoa, of which the capital Genoa was being besieged by a joint Franco-Savoyard army composed of 30,000 men and 3,000 cavalry. In 1625, when the Republic of Genoa, traditionally an ally of Spain, was occupied by French troops of the Duke of Savoy, the city underwent a hard siege. It was known in Genoese governmental circles that one of the reasons why the Dutch government had offered their help to the Franco-Savoyan army was so that they could "hit the bank of the King of Spain". However, the Spanish fleet commanded by General Álvaro de Bazán, Marquis of Santa Cruz, came to the aid of Genoa and relieved the city. Returning its sovereignty to the Republic of Genoa and forcing the French to raise the siege, they consequently began a combined campaign against the Franco-Savoyan forces that had overrun the Genoese Republic one year before. The joint Franco-Piedmontese army was forced to leave Liguria and Spanish troops invaded Piedmont, thereby securing the Spanish Road. Richelieu's Invasion of Genoa and the Valtelline had resulted in his humiliation by the Spaniards.
Answer this question: what type of join Franco Piedmontese army?
Liguria