Final answer:
Commodore Matthew Perry's display of military force and the looming threat of intervention, coupled with internal pressures and the desire to avoid the fate of other Asian nations, led Japan to accept Fillmore's letter and sign the Treaty of Kanagawa, ushering in the Meiji Restoration and Japan's period of modernization.
Step-by-step explanation:
The Japanese government accepted the letter from President Fillmore brought by Commodore Matthew Perry in 1853 largely because of the show of military force and the potential threat of military intervention that accompanied it. Perry's squadron of warships entered Edo (Tokyo) Bay and demonstrated a willingness to exert military power by firing blanks towards the shore, something the Japanese military at the time could not effectively counter. Moreover, Japan's seclusion policy had been steadily unraveling due to pressures from within, such as the desires of southern daimyo for foreign trade, and from without, like the colonization happening in neighboring China.
Realizing their inability to compete against industrialized nations and to protect against future aggression, Japan signed the Treaty of Kanagawa on March 31, 1854. The treaty opened two ports for American use, established a U.S. consulate in Japan, and arranged for the humane treatment of shipwrecked sailors. This set forth a period of rapid modernization and westernization in Japan, known as the Meiji Restoration, during which Japan sought to build its military and industrial capabilities to avoid the fate of countries like China.