Why did merchant guilds form in the middle ages?
to serve local churches
to build cathedrals
to eliminate competition between merchants
to protect merchants and their goods

I believe the answer is: To protect merchants and their goods

During the middle ages, it is very common for the goods that being distributed by merchants to be robbed by bandits in the middle of journey. Because of this, merchant guild was created. They handle such problems by providing mercenaries army to guard the distribution process.

(202 bc - 220 ad) dynasty started by lui bang; a great and long-lasting rule, it discarded the harsh policies of the qin dynasty and adopted confucian principles; han rulers chose officials who passed the civil service exams rather than birth; it was a time of prosperity