what is the peasant's crusade?

Answer 1

In Clermont, in 1095 CE, Pope Urban II called upon Christians to reclaim the Holy Land (Israel, Palestine, Jordan & Syria of today) for Christianity.

Apparently riled up by the Pope's speech, or by accounts of it, many of the ordinary European Christians living in the area - rather than the lords who had supported the idea loudly at the Pope's speech - launched a poorly organized attack on the Muslim part of Constantinople (probably about the beginning of 1096).

On their way, they attacked Jewish neighborhoods, raided farms for supplies (apparently ignoring the faith of the farmers), and made themselves unwelcome throughout the Balkans.

When they arrived at western, Christian-held Constantinople, the emperor had them quickly ferried across the Bosporous to their doom at the hands of the Caliph's army.

It's hard not to be dismissive of such an inglorious and hateful enterprise, but bear in mind that it was followed by much better funded and better armed missions of war, which met with much initial success, and ultimately failed to reclaim the Holy Lands for any single religious group.