For what purposes did merchants unite in guilds? What role did the Hansa play in international trade?

Guilds were associations of medieval merchants that helped them to fight competitors and at the same time take measures against monopolization of the market, help needy brethren, establish uniform rules for trade, ensure and protect the privileges of their members, even defend against attacks by pirates and other robbers. One of the most influential merchant associations was the Hansa, or the Hanseatic League, which united trade and craft cities throughout northwestern Europe (including Veliky Novgorod and Pskov) and traded in Russian furs and wax, English wool, cloth from Flanders, etc.