He still retained them in 1624, when the Grison lords, seconded by a French re-enforcement under the orders of the Marquis of Ceeuvres, attacked the feeble garrison of the Valteline; in a few days they were masters of all the places in the canton; the pope sent his nephew, Cardinal Barberini, to Paris to complain of French aggression, and with a proposal to take the sovereignty of the Valteline from the Grisons; that was, to give it to Spain.

"Besides," said Cardinal Richelieu, "the precedent and consequences of it would be perilous for kings in whose dominions it hath pleased God to permit diversity of religion." The legate could obtain nothing.

The Assembly of Notables, convoked by Richelieu in 1625, approved of the king's conduct, and war was resolved upon.

The siege of La Rochelle retarded it for two years; Richelieu wanted to have his hands free; he concluded a specious peace with Spain, and the Valteline remained for the time being in the hands of the Grisons, who were one day themselves to drive the French out of it.
Whilst the cardinal was holding La Rochelle besieged, the Duke of Mantua had died in Italy, and his natural heir, Charles di Gonzaga, who was settled in France with the title of Duke of Nevers, had hastened to put himself in possession of his dominions.

Meanwhile the Duke of Savoy claimed the marquisate of Montferrat; the Spaniards supported him; they entered the-dominions of the Duke of Mantua, and laid siege to Casale.
When La Rochelle succumbed, Casale was still holding out; but the Duke of Savoy had already made himself master of the greater part of Montferrat; the Duke of Mantua claimed the assistance of the King of France, whose subject he was; here was a fresh battle-field against Spain; and scarcely had he been victorious over the Rochellese, when the king was on the march for Italy.