The motivation for the various crusades differed.
The first crusade was to a large extent a response to the increasing power of the Muslim empire. This seemed to have worries Christian powers for some time, and when the Byzantine Emperor asked for military help from the Pope to fight off turkic muslims the Pope responded with a speech at the Council of Clermont calling for all Christians to help the Christians in the east to fight the Muslims.
This crusade was successful, partly because the Muslim leaders did not recognize that there was a religious element to the invasion, and that the ultimate aim was to "liberate" the holy land from the Muslims. They instead just treated it as another element in the internal fights that was already going on within the Muslim leaders anyway. Therefore there was no concerted Muslim response, and the Christians could pick off local rulers one by one.
(ref: Amin Maalouf, "The Crusades Through Arab Eyes")
So the motivation for this crusade was mostly political, although since that politics to a large extent was about increasing the power of the Catholic Church and stopping the expansion of Islam, that politics has a religious part to it. Some of those who took part may in addition have had religious reasons, but most of those who took part tended to do so to grab land and loot.
The second to ninth crusade was attempts to reconquer land that was taken in the first crusade but subsequently lost. As the crusader states that were established after the first crusade quickly lost any pretense to have a religious motivation and just became a part of the local power politics, fighting with other local leaders and often even intermarrying with Muslims, the attempt to re-conquer these lands could use religious reasons only as pretext.
They were therefore fully politically motivated, in any reasonable meaning.
Then there were any other minor crusades. The Northern Crusades and The Albigensian Crusade had a similar mix of politics and religion as the first crusade, politics in as much as it was about extending the power of Christian leaders, and religious in as much as it was about spreading Christianity (or in the case of The Albigensian Crusade, to get rid of a heretical Christian sect).
The Aragonese Crusade was purely political, as it was a Pope vs a Catholic king.
So, in summary, mostly political, but since there was no separation of church and state at this point, there was a religious facet to some of the crusades.