Later in the early 18th century, the za gained in influence by working more closely with the Tokugawa government; this brought more centralization and a return to their monopoly power.
Though very powerful at times, and enjoying certain tax exemptions and other formal governmental benefits, it is important to note that the za, at least in their original forms, were never as official or organized as the medieval guilds of Europe.
During this period, agricultural and economic advancement and growth was rapid in the countryside, or "Home Provinces", and za began to conglomerate into groups organized by their locality, not by their trade.
These rural za were generally associations of wealthier peasant farmers who combined to sell oil, bamboo, rice, or other agricultural products in bulk; they occasionally allowed urban brokers to join their guilds, to act as their proxy or guide in the city markets.
Towards the end of the Muromachi period, the za began to grow independent of the noble families, temples, and shrines they had placed themselves under, having grown large enough and powerful enough to protect themselves.
Towards the end of the 16th century, one hundred years into the Sengoku period, Oda Nobunaga briefly took command of the country, and established "free" markets and guilds, known respectively as rakuichi (楽市) and rakuza (楽座).
Another type of trade group, called toiya (or ton'ya in Edo), served as wholesale merchants, focusing primarily on shipping and warehousing.
At this time, Osaka came into its own as a great port, and eclipsed Kyoto as the nation's primary center of trade, contributing further to the downfall of the original za.
This centralization made monopolization of the industry far easier, and brought significant wealth to the Kyoto government and to the merchant members of the various trade organizations.