I like Prague in Black and Gold. I also co-host a podcast on Czech history called Bohemican.

Otherwise you're asking a super broad question.

The history goes back to Greater Moravia. That might be a good thing for you to look at.

It became a part of the Holy Roman Empire (the only Kingdom in the HRE) and later the Austrian Empire with bouts of independence here and there (see the Hussite Wars, for instance)

But the whole time they were Czechs (i.e. Slavs), not German, so they wanted independence.

I'm not what you mean about migration. Along with other Slavic peoples they moved West. How and why is mostly legendary (see Father Czech if you're curious)

They weren't ever part of another culture, so I'm not sure what you mean. They were next to - or under Germans/Austrians for so long that Czechs have a more similar culture to Bavaria or Austria than Russian.. but I can't tell what you mean.

If you ask more specific questions I'd be happy to try and help.

Could you be more specific? Why call their history sordid? What do you mean about becoming another culture? By your first question, do you mean how did Czechoslovakia split, or how did Czechs (and Slovaks) found a republic after the dissolution of the Austrian monarchy following the Great War? Please provide more detail.