If Europe had had a supply of elephants we can be sure that they would have been tried out at least in the early medieval times. But since the Muslims blocked the way to all areas of elephants there was no chance to get them other than as curiosities (I believe one of the Caliphs sent one to Charlemagne as a gift).
And since the Muslims didn't us them there wasn't any tradition of fighting with or against them. So in essence the rulers of Europe hardly knew that they could be used for warfare (a few might have read about the Punic Wars).
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