I am aware the Emperor Meiji abolished the Samurai class during the reformation. Why did he do so? How was it enforced?
The Charter Oath promulgated at the enthronement of Emperor Meiji of Japan on 7 April 1868 includes several parts that identify the reasons for the radical social restructure that followed the Meiji restoration and an indication of the motivations for the dissolution of the warrior class that had been a defining characteristic of Japanese society.
The determination to remove the "base customs" of the past drove the new government to dismantle the old Confucian based social order. This included the removal of the restrictions and privileges that had defined the samurai, peasant, artisan and merchant classes.
During the summer of 1869 Tokyo formally reclassified the population as nobles, former samurai and commoners.
In 1871 the Tokyo government assumed the responsibility for paying stipends to the former samurai. This immediately accounted for almost one-third of the government's expenditure. This massive financial obligation created pressure to abolish the subsidies entirely.
Despite less than universal support amongst the new leaders, in 1873 the Daijō-kan (department of state) offered interest-bearing goverment bonds to former samurai who surrendered their stipends. Three years later it made that exchange obligatory.
In 1876 ex-warriors were deprived the right to carry swords.
These steps to dissolve the military estate coincided with the establishment of a conscript army based on the Prussian and French models. Vice minister of military affairs Yamagata had seen the efficacy of these armies first hand in Europe and in 1873 enacted a Conscription Ordinance:
This landmark measure was a major step in the disfranchising of the samurai estate and vastly strengthened the regime's authority by creating a force capable of dealing with countercoups and providing internal security.
Quotes and references from:
James L. McClain. Japan, a modern history W.W. Norton & Co, 2002
... and as Steven I think implies, the power of the samurai continued in the Japanese Army. This was one reason why the army had no problem doing all their evil in the name of the 'Emperor', while actually doing everything they could to ensure his opinion was never allowed to interfere. This reflected previous Japanese history when Emperors were puppets of the shogun.
This appears to have happened roughly around 1873, when Emperor Meiji decided to change his military structure to use a conscripted army. He was attempting to modernize Japan by following the examples he had seen from England and Germany. Most of the Samurai volunteered to become soldiers and many eventually became officers in the new modernized Japanese army. By eliminating the Samurai, the emperor was also attempting to eliminate the feudal domains that had separated the country into different political domains, thereby reinforcing support for his centralized government.