He did not improvise or change, led to Burnside losing the Battle of Fredericksburg.
Regardless, religion was always the primary trigger for a crusade. Though religion always played a part, the perceived threat to the church evolved. The first Crusade focused solely on ridding the Holy Land of Muslim forces. The popes began to use crusades to combat any perceived threat against the Catholic Church.
It would be "Robertson," who was not a European religious reformer, at least not on the same level as Luther and Calvin, since these two ushered in eras of massive reform.
