I don't get how Ska is connected to the punk/rock side of things. I don't mind it but where did that come from to connect the two?
It's basically just an accident. Some punk guys got into reggae and ska in the 70s. It was briefly a symbol of racial harmony but I think it lasted because the musical styles are weirdly complementary. Punk rockers don't get to have ballads, so they dabble in ska instead. Something like that.
I would also guess that the whole 2-tone thing was going on in England in the late '70s, and it would be difficult for a musical subculture (especially one with political roots) to not sort of crash into punk rock and skinhead culture and stuff at the time?
Then again, I was not even close to being alive at that point, so what do I know?
(Answer: Very Little.)
I think that's all part of it. The emigration of Caribbean people to England in the 50s and 60s put the underclasses of different races in close proximity for the first time (in England), and you had skins and mods first identifying with ska and soul, and then as punk and reggae emerged in the 70s, another level of identification. English ska band Symarip had, "Skinhead Moonstomp,", English reggae bands like Steel Pulse and Aswad played with punk bands frequently early on, Bob Marley had "Punky Reggae Party," etc. And from the other side, the Clash, Slits, and Ruts were being directly influenced by events in their own neighborhoods (Brixton riots, Notting Hill riots, etc.), and were reflecting that back in their affinity for and use of reggae. With the Specials, it's a little less organic, but kind of more interesting - they were all in various non-ska bands around Coventry, got together as a punk band, and then led by Jerry Dammers, they got out of just being a punk band as a direct reaction to months of violence at every single show, and they made a very conscious decision to create this "Two-Tone" imagery and present themselves as a true synthesis of complementary colors, ideas, and musical influences - actually trying to "bring people together." It was a high-minded concept, and was willfully trying to cement this punk and ska alliance. As with everything, a lot of what came in its wake (especially in the 90s) was crap, but...
Read this book!
Cut and Mix, by Dick HebdigeThere are chapters on ska, Two-Tone, and punk and reggae.