I actually wrote my undergraduate thesis on this and will happily provide sources if asked because I am absolutely in love with this subject.

Originally, Bohemia had been made a nominal subject of Charlemagne in the late 8th century, but this was not important at the time (it later became important, though, in the establishment of tradition). Christianity came to Bohemia in the 8th century, but it wasn't until Saint Kyril (of the famous duo Sts. Kyril and Methodius) in the mid 9th century that Christianity became the dominant religion. Kyril was Byzantine Greek and so he taught the Czech people (and, with his brother, nearly all of the Slavic peoples) a pan-slavic identity based on a proto-slavic language to which they invented the Old Church Slavonic alphabet (based on Greek). At the same time as Greek christianization pushed north and westward, German christianization, spurred onward by the ever-present "drang nach osten" (push to the east, a very important concept in early German studies), pushed eastward and they fought one another over the "right" way to spread the religion. The Pope officially endorse Latin and so after a decades long struggle, the Czechs (and the Poles) fully adopted the Latin script and the Latin church. This was what fully pulled Bohemia permanently looking westward and so determined its relationship with the German empire (later the HRE). Bohemia would, by the mid 10th century, take place in major battles on behalf of the Ottonian dyansty, most notably against the Magyars.

At the same time, the Czechs had an extremely complicated relationship with the empire during this period. Although the head of bohemia was technically called a "duke", this title existed only so that it could be bestowed by the emperor, rather than as a reflection of the sovereignty of Bohemia. Bohemia was almost entirely independent and exercised its independence quite regularly throughout the 10th and 11th centuries.

The creation of the Bishopric of Prague in 973 was meant by the Czech duke as both a gesture of solidarity with the German emperor but also as a way for the duke to have German support in his long and bitter struggle with the ruling family of the Czech (although possibly Polish) nobility, the Vrsovici, who at this time were trying to overthrow the current dynasty.

This backfired and, while the duke remained in power, he lost much of the support of his people, and so ended up worsening his good relationship with the Germans that he had created with the establishment of the Bishopric of Prague. On two separate occasions, he accidentally took the field against the emperor, and both times Germany turned closer to Poland. Eventually Poland had become a closer ally of Germany than Bohemia was, which began a period of long Czech-Polish rivalry.

in 1002, the German emperor, Otto III, died and the Polish duke, Boleslav I Chrobry (just a side note: I haven't been mentioning Czech names because there are 5 different Boleslavs in this story and it would be impossible for me to expect you to keep them straight. Boleslav here will ONLY refer to the Polish duke) backstabbed Germany and invaded the eastern empire. The also invaded the entirety of Bohemia, blinded and overtrhew the duke of bohemia, annexed the territory and installed Boleslav of Poland as king of the Czechs. This was greatly insulting to the Czechs who, having been thoroughly defeated, were forced to be ruled by their hated rivals. Leading an army of Germans, endorsed by the emperor, the exiled son of the former Czech duke led a campaign to take back his fathers empire and, with German support, succeeded in finally defeating Poland.

This united push against a hated enemy is what enabled successive Czech dukes to continue fostering a positive relationship with the German empire, as well as the Latin patrimony. This culminated in the crowning of Czech duke Vrastislav as King of Bohemia in 1085, through the office of the Emperor Henry IV.

There's a whole hell of a lot more to this story and I've simplified a lot of it for you. I can explain anything in detail if you want :)