Tenpo (aka Tenpu) refers to what the Edo bakufu (Japanese feudal government headed by the seii taishogun [literally, "great general who subdues the barbarians"]) changed daimyo's (Japanese feudal lord) territories to different locations. Tenpo is almost a synonym for Kunigae and Ifu.
The terms such as 'Kunigae,' 'Tokorogae' and 'Tokutai' were used in records instead of Tenpo.
Tenpo was one of the powers of disposition and control that the unified authority had over all the daimyo in modern times.
After the Taiko kenchi (Hideyoshi TOYOTOMI's nationwide land survey), Tenpo were enforced based on the concept that the Shogun, who was also called Tenkabito (person becoming the ruler of the country), had ultimate ownership of even daimyo's territories.
However, territories were often changed with additional properties, so Tenpo is not categorically described as disposition and control.
In the Edo period, the bakufu started to enforce Tenpo, and in the early of the period, the basic policy of Tenpo was to transfer the Tozama daimyo (nonhereditary feudal lord) to regional areas and to transfer the daimyo on the Tokugawa clan's side (called the Shinpan [Tokugawa's relatives] and the Fudai [hereditary vassals]) to the former territories of the Tozama daimyo.
After the middle of the period, Tenpo of the Tozama daimyo extremely decreased, and administrative Tenpo of the daimyo on the Tokugawa clan's side on their appointments in the bakufu's posts became mainstream.
On the other hand, it is a fact that Tenpo took away the aspect of zaichi ryoshu (resident landlords) from samurai, playing a role in promoting the transition from the Jigatachigyo system (provision of lands from a feudal government or domains to retainers as salary) to the horoku system (salary).
This was a very important event for the kinsei ("early modern") daimyo in heading their vassals, and this is also one of the elements that distinguish the Kinsei daimyo from the Sengoku daimyo (Japanese territorial lord in the Sengoku period).
For the people including peasants, Tenpo meant what the rights they had acquired before would be denied due to the changes of their feudal lords, so the people sometimes staged opposition uprisings. The Tenpo Hatto (The laws for changing the territory) had the words about nonpayment of tribute and the loss or damage of a borrowed thing, so land sales contracts came to contain the words to reject debt cancellation orders at an early stage.
Tenpo was the bakufu's absolute authority over all the daimyo during the Edo period, so the failure in 1840 of changing three daimyo's territories one another at the same time symbolized the diminishing authority of the bakufu.