While the origin of manga dates back to as far as the 12th century. Pre-war manga magazines, like Eshinbun Nipponchi and The Japan Punch were attempted, but their sucesses were mixed, and mostly unsuccessful for a variety of reasons. The hardly resembled manga today, but mores resembled picture books of text, more synonymous with Chinese graphical art of the periods.
The media we refer to as modern manga, was mostly born though the commercialism of post-war Japanese economy. Western influences particularly American culture played a big role. How it all came about is due a variety of factors, but the wave of commercialism is what helped carry it around the world.
Manga itself is an immersive social environment that encompasses various social aspects, from history, to language, to politics, religion, family, economy, and education, manga reflects Japanese society at its core, the good and the bad. The myths, traditions, beliefs, rituals, taboos, and fantasies of Japanese life are laid bare on pages of paper. The commercial proliferation of the Japanese publishing industry created a channel of expression that allowed the for the mass distribution of both real and fantastical ideas of the time. Manga as a medium is most relatable to people on a personal level because of this. While not always applicable the intimate ideas and subjects covers by the media connect to many on a personal level. While manga tends to depict a microcosm of Japanese Society. It's problem are not limited to Japanese people and society. These joys, sadness and tribulations can be share by all as fellow humans who can empathize.
Manga is a medium of expression for people to other people. People might not see eye to eye all the time, but when they do, the connection they make go beyond the images and words on the page.