In 1991, Pope John Paul II opposed the Gulf War and publicly appealed to U.S. President George H.W. Bush not to wage it. In 2003, he once again opposed a war in Iraq and appealed to U.S. President George W. Bush to refrain from going to war.

In an Address to the Diplomatic Corps at the Vatican on January 13, 2003, the Pope declared that “War is never just another means that one can choose to employ for settling differences between nations” and reiterated that “war cannot be decided upon . . . except as the very last option and in accordance with very strict conditions.”

Two months later, on March 16, 2003, in his Angelus Message, Pope John Paul spoke of the need “to work with responsibility for peace” and declared that all options had not been exhausted: “There is still time to negotiate; there is still room for peace, it is never too late to come to an understanding and to continue discussions.” The war began two days later, on March 18, 2003.

Pope John Paul did not drop his opposition to the war once it had started. On June 4, 2004, in an Address to President Bush (who was visiting him at the Vatican), the Pope reminded the President that:

"You are very familiar with the unequivocal position of the Holy See in this regard, expressed in numerous documents, through direct and indirect contacts, and in the many diplomatic efforts which have been made since you visited me, first at Castelgandolfo on 23 July 2001, and again in this Apostolic Palace on 28 May 2002."

Benedict XVI on the War in Iraq
Since being elected pope, Pope Benedict XVI has largely confined his remarks on Iraq to prayers for peace, though he has occasionally been critical of the conduct of the war. In the April 2003 issue of 30 Days, an Italian Catholic magazine, the future pope (then Joseph Cardinal Ratzinger) made his opposition to the war known, while supporting Pope John Paul’s assessment of the justice of the war. He declared Pope John Paul’s position on the war to be “the thoughts of a man of conscience occupying the highest functions in the Catholic Church” and “the appeal of a conscience enlightened by the faith.”

Cardinal Ratzinger also argued that “reasons sufficient for unleashing a war against Iraq did not exist,” in part because:
"proportion between the possible positive consequences and the sure negative effect of the conflict was not guaranteed. On the contrary, it seems clear that the negative consequences will be greater than anything positive that might be obtained."