What was the effect of the union of church and state during the Middle Ages?

During the Middle Ages, typically accepted to fall between 476 AD and 1453 AD, the Roman Catholic church in particular gained power, as it became highly organized and served to meet not only people's spiritual needs but their social needs as well.
As the church grew during the Middle Ages, it encouraged people to donate to its causes and even heavily imposed indulgences as a monetary means of forgiveness for sins. Because of these monetary gains, the church amassed a fortune in both money and land during this time. Large cathedrals were built that showcased the grandeur of wealth that the church possessed; this stood in sharp contrast to most people, whose meager means of living provided the means for such constructions.
The result was that the Church had enough power to be a political force. Church leaders and political leaders created laws together. Bishops often had a close enough relationship to kings that they were trusted to enact laws on the king's behalf. This also reflects that kings of this period were seen as ruling through divine authority; they believed that God himself had provided the power given to them through their ordination. Around the 10th century, the Pope declared that he had the right (and power) to replace kings around Western Europe.
This also led to the Crusades. Some estimate that at least a million people died as Christians tried to reclaim lands of political importance that had been lost to Muslim invasions.