Firstly, it needs to be noted that the issue of the delay is misleading for a number of reasons. The subject is usually linked to the popular misconception that she was never considered a saint before that point, as well as the related notion that the delay represented widespread opposition to her within the Church. This in turn is based on the misconception that a long delay is unusual. I'll cover all of these issues below:

Since all martyrs are essentially automatically considered saints, even without a formal canonization process, it might be said that she was effectively pronounced a saint at that point.

Far too many authors have claimed that the Appellate court never issued any statements concerning Joan of Arc's spiritual status, an egregious error of historical fact. (The Inquisitor-General's comments on her martyrdom occur in Part I Ch 9 of his "Recollectio", written in June of 1456 - for the original Latin, see DuParc's "Procès en Nullité...", Vol II, p. 509.) The view of her as a martyr and saint was fairly common during that era.

In 1452 a Cardinal of the Church, Guillaume d'Estouteville, declared that any person who attended the religious play in Joan's honor at Orleans (which had been performed since c. 1435) could thereby gain an indulgence from the penalty of sin - precisely as if this act were something akin to a pilgrimage to a saints' shrine or other holy site, since indulgences are only awarded for such acts of piety. This indulgence was periodically renewed after that point by local bishops.

The above mentioned religious play presented her, judging from the surviving text of the script, as a living saint who was sent by God, reflecting the common attitude of the people at Orleans and throughout those portions of France which supported Charles VII's faction.

Even some members of the opposing faction viewed her in a similar fashion - in 1440, a pro-Burgundian clergyman named Martin le Franc included her in a book called "Le Champion des Dames" in which the hero compares her death to that of Christ. A more detailed examination of some of these issues can be seen in a recent article in the "Joan of Arc Primary Sources Series", at: http://primary-sources-series.joan-of-arc studies.org/PSS021806.pdf

Similar comments can be made concerning the claim, cited by many authors, that the Church entirely ignored her up until the late 19th century.

Aside from the above mentioned examples of both popular and ecclesiastical devotion, Pope Pius II wrote an approving piece about her in his Memoirs in the late 15th century; she was subsequently utilized by the 16th century Church as a symbol of the Catholic League during the wars of religion between Catholics and Protestants.

Numerous books about her were written by clergy as well as laity throughout the period in question. The chief change which occurred in the 19th century was merely an additional surge of interest due largely to the research conducted by a secular historian named Jules Quicherat, whose five-volume series on the primary source documents led to an increased study of her life by other authors and therefore the publication of a larger quantity of books on the subject. This interest in turn helped fuel the push for canonization in that era, a trend which was further accelerated by Joan of Arc's popularity during WWI and the French-English alliance during that war (a topic which I'll deal with farther below).

All canonization processes are initiated by "grassroots" petitions, and they generally do not go forward without considerable popular support.

400 years to canonize St. Thomas More;

707 years for St. Agnes of Prague,

364 years for St. Nicholas Owen;

409 years for St. Agnes of Montepulciano,

448 years for St. Norbert,

500 years for St. Agnes of Assisi,

316 years for St. John Southworth;

717 years for St. Hermann Joseph,

364 years for St. Thomas Garnet; etc.

St. Hildegard still has not been officially canonized after some 830 years, although she is considered a saint and in fact was considered as such during her own lifetime.

As seen from the above list canonization often is not a speedy process.

Concerning any political reasons for the delay in Joan of Arc's canonization: while there were (and still are) always numerous political controversies connected with her, it's difficult to find a direct linkage between the political issues and the delay in her canonization. It might be noted, however, that English opinion was a concern: when the initial stage of the process was begun, the Pope is alleged to have taken the unusual step of first consulting Queen Victoria (a Protestant monarch, no less) to make sure that the English government had no objections.

It may not be coincidence that she was canonized shortly after World War I, during which the English and French had been allies. That war had witnessed considerable interest in Joan of Arc by Allied troops - soldiers carried her image with them into battle; a popular song ("Joan of Arc, They Are Calling You") asked her to return to earth in order to save France. French troops in one sector of the front misinterpreted an image projected by a German searchlight to be Joan hovering in the skies, blessing their efforts. Her canonization came only two years after the armistice was signed ending the war.