The war with France simmered on until the Truce of Nice, intended to be for ten years, signed between the two powers in 1538.

In 1544 war broke out again, and fortune again favored Charles.

He invaded France almost to the gates of Paris, but did not press his advantage and on September 18 signed the Peace of Crepy giving up all his conquests.
Unable to turn his arms against the heretics, Charles continued to negotiate with them.

The pressure he brought to bear upon the pope finally resulted in the summoning by Paul III of a council to meet at Mantua the following year.

[Sidenote: June 2, 1536] The Protestants were invited to send delegates to this council, and the princes of that faith held a congress at Schmalkalden to decide on their course.
[Sidenote: February 1537] Hitherto the Lutherans had called themselves a part of the Roman Catholic church and had always appealed to a future oecumenical or national synod.