The alternate attendance system, or sankin-kotai, was a Tokugawa Shogunate policy that required daimyo (or provincial lords) to divide their time between the capital of their own domain and the shogun's capital city of Edo (Tokyo). The tradition actually began informally during the reign of Toyotomi Hideyoshi (1585 - 1598), but was codified into law by Tokugawa Iemitsu in 1635.
Actually, the first sankin-kotai law applied only to what were known as the tozama or "outside" daimyo. These were lords who did not join the Tokugawa side until after the Battle of Sekigahara (Oct. 21, 1600), which cemented Tokugawa power in Japan. Many of the lords from distant, large, and powerful domains were among the tozama daimyo, so they were the shogun's first priority to control.
In 1642, however, sankin-kotai was also extended to the fudai daimyo, those whose clans had been allied with the Tokugawas even before Sekigahara. A past history of loyalty was no guarantee of continued good behavior, so the fudai daimyo had to pack their bags as well.
Alternate Attendance System
Under the alternate attendance system, each domain lord was required to spend alternating years in their own domain capitals or attending the shogun's court in Edo. The daimyo had to maintain lavish homes in both cities and had to pay to travel with their retinues and samurai armies between the two places every year. The central government insured that the daimyo complied by requiring that they leave their wives and first-born sons in Edo at all times, as virtual hostages of the shogun.
The shoguns' stated reason for imposing this burden on the daimyo was that it was necessary for national defense. Each daimyo had to supply a certain number of samurai, calculated according to the wealth of his domain, and bring them to the capital for military service every second year. However, the shoguns actually enacted this measure to keep the daimyo busy and to impose hefty expenses on them, so that the lords would not have the time and money to start wars. Alternate attendance was an effective tool to prevent Japan from slipping back into the chaos that characterized the Sengoku Period (1467 - 1598).
The alternate attendance system also had some secondary, perhaps unplanned benefits for Japan. Because the lords and their large numbers of followers had to travel so often, they needed good roads. A system of well-maintained highways grew across the entire country, as a result. The main roads to each province were known as the kaido.
The alternate attendance travelers also stimulated the economy all along their route, buying food and lodging in the towns and villages that they passed through on their way to Edo. A new kind of hotel or guesthouse sprang up along the kaido, known as honjin, and built specifically to house the daimyo and their retinues as they traveled to and from the capital. The alternate attendance system also provided entertainment for the common people. The daimyos' yearly processions back and forth to the shogun's capital were festive occasions, and everyone turned out to watch them pass. After all, everybody loves a parade.
Alternate attendance worked well for the Tokugawa Shogunate. During its entire reign of more than 250 years, no Tokugawa shogun faced an uprising by any of the daimyo. The system remained in force until 1862, just six years before the shogun fell in the Meiji Restoration. Among the leaders of the Meiji Restoration movement were two of the very most tozama (outside) of all the daimyo - the restive lords of Chosu and Satsuma, at the very southern end of the main Japanese islands.