The Tokugawa Shogunate came into power in 1603 when Tokugawa leyasu, after winning the great battle of Sekigahara, was able to claim the much sought after position of Shogun. They continued to rule Japan for the next 250 years.
There was a combination of factors that led to the demise of the Tokugawa Shogunate. The advantages that the rule of the Tokugawa bought to Japan, such as extended periods of peace and therefore the growth of trade and commerce was also the catalyst that bought this ruling family to its demise.
As the Merchant class grew wealthy the samurai who had always been the ruling class were sinking into poverty, this was caused as a direct result of the now peaceful conditions the country was experiencing. No longer needed to defend their local lords and emperor the samurai had to find other occupations to practice in, as they also found themselves in debt because of this change in profession they were obliged to borrow from the despised merchant class.
This led to a breakdown in the social hierarchy that was so firmly entrenched in Japanese culture, as the merchants because of their newfound wealth began to marry above their designated class. Along with the fall of the samurai from their once exulted position, the daimyo role also changed because of constrictions and expectations placed on them by the Tokugawa government. Trying to maintain this expensive way of life led to an increase of tax on the peasant class combined with famine and debt it was not surprising that uprisings became more frequent .
As well as growing internal unrest within the country, Japan was now being targeted by foreign interest. This reached a climax in 1853 when Commodore Perry delivered a letter to Japan requesting (demanding) friendship and trade. The eventual capitulation of the Shogun to resume trade with westerns outraged many Japanese who saw it as sign of weakness and loss of political power. Opposition clans bonded together to overthrow the Shoguns who had lost the respect of most Japanese.
This loss of control of the populace through all classes and the increasing presence the western world eventually proved too much and allowed the Satsuma and Choshu opposing clans to restore imperial administration. This led after some minor warfare to the resignation of the last Shogun.
I think we can determine from this slice of history that a ridged government does not necessary cause things to stay stagnant but almost because of it inflexible position eventually brings about it own decline.