Haha, this feels a lot like homework and my policy through university and graduate school was to simply not do assigned homework.
Nevertheless, let's give it a shot.
This is my impression based not only on the game, but also from subsequent content I have been exposed to after having played the game (based on my interest in the game factions - Oda, Hojo, Toyotomi, Uesugi, etc.).
Upon exposure to foreign culture (after the landing of the black ships), the shogunate worried about the influence of foreign ideas on its populace. They also recognized the value of foreign technology (e.g. guns in the game). So they limited foreign interactions to mercantile activity on the island of... the name escapes me (something-jima).
This policy continued for... a couple of centuries? But started to fall apart before the era depicted in media such as The Last Samurai.
Now I will admit that my understanding of the events and impact is somewhat superficial. It may also be inaccurate, in which case I am sure you will correct me. But my understanding would have been non-existent if not for the game.