After being closed under military rule for almost 60 years, Japan was forced to open to the world to catch up with the rest of world in military and technology. The government they made was a lot like OTL US's government, except for the fact that you only get one term.
They have a strong military, due to the invasions by China in GWII. In the 60's, Japan was invaded and had a puppet government set up by China, and was called North Nippon. This was what brought them into GWII.
Today, Japan is extremely ahead in tech, with new innovations in life extension and robotics. It invented things like anime in more recent time, which was based on old English animations.