He would send Chinese sleeper agents to all of the monarchies all over the world to kidnap all the princesses for him and his 8 sons to marry. The UN would send him a strongly-worded letter and probably put sanctions on the newly formed Koopa's Republic of China. Bowser then orders Italy hand over the Mario bros for they are wanted for conspiracy to commit crimes against the his government. Everyone laughs this off, but Bowser responds by flying military aircraft over Taiwan to show the world that he is serious.
In a nutshell, China under Bowser's rule probably becomes a more powerful North Korea. Or something like that.