[2] Realizing the danger, in 1623, Venice, the Duke of Savoy, and France formed an alliance to capture this strategic position by signing the Treaty of Paris (1623).

France did nothing as the Papal troops of Gregory XV established control over Valtelline due to the lackluster policies of Charles de La Vieuville.

Richelieu had no difficulty in persuading Louis XIII that if Spain gained control of the Valtellina valleys, it would unite them with possessions of the house of Austria, doubling the power of this house, and remove the only obstacle to its universal domination, exposing the independence of all of Europe, "shackling Christendom, making the Pope the chaplain of the Habsburgs", and excluding France from Italian affairs.

[4] The Pope could not afford to lose the crucial forts in the Valtellina and began to organise a force of 6,000 men to retake the valley.

Urban VIII sent Cardinal Francesco Barberini, who was his nephew, as legate to Paris to seek peace in 1625; he was also authorized by Spain.