Which French king led the Second Crusade?

The French king who led the Second Crusade was Louis VII of France. He joined the expedition after the County of Edessa, the first crusader state established during the First Crusade, fell to the forces of Zengi in 1144.

Louis announced his intention to undertake the campaign at Bourges in 1145 and later received papal support from Pope Eugene III. Bernard of Clairvaux became the crusade's most influential preacher, helping recruit participants across France. Louis traveled east with his wife, Eleanor of Aquitaine, while Conrad III led the German contingent.

The crusade began in 1147. Both royal armies suffered severe losses crossing Anatolia, and the surviving forces eventually reached the Kingdom of Jerusalem. In 1148, Louis, Conrad, and the leaders of Jerusalem attacked Damascus, but disagreements over strategy and the city's strong defenses forced them to abandon the siege after only a few days.

Louis's participation is sometimes overlooked because Conrad III was the other principal monarch of the eastern expedition. However, when the question asks specifically for the French king, Louis VII is the single canonical answer. The Second Crusade ended in 1149 without recovering Edessa, although campaigns in Iberia achieved important successes.