Why were the Chinese Christians such targets of rage during the Boxer Rebellion?
Generally speaking, Christianity was a threat to traditional Buddhist/Confucianist beliefs and attitudes within Chinese society. However, the Shandong drought provided the specific catalyst that set off the anti-Christian Boxer movement.
Traditionally, entire communities would come together during times of drought and pray to the gods and ancestors for rain. However, those villagers who had converted to Christianity refused to participate in the rituals; their neighbors suspected that this was the reason that the gods disregarded their pleas for rain.
As desperation and mistrust grew, rumors spread that the Chinese Christians were slaughtering people for their organs, to use as ingredients in magical medicines, or putting poison in the wells. Farmers genuinely believed that the Christians had so displeased the gods that all of the region was being punished with drought. Young men, idled by the lack of crops to tend, began to practice martial arts and eye their Christian neighbors.
In the end, an unknown number of Christians died at the hands of the Boxers, and many more Christian villagers were driven from their homes, like those pictured above. Most estimates say that "hundreds" of western missionaries and "thousands" of the Chinese converts were killed, by the time the Boxer Rebellion ended.