Obviously want someone to elaborate on this but isn't Christianity itself a breakaway from Judaism?

It has, just not many sucessful or well known ones (Well except Christianity but I'm not going to write about that).

In the times of the second temple Judaism was relatively splintered and it included the Pharisees, the Sadducees and the Essenes.

The Pharisees (comes from לפרש in Hebrew which means interpret) believed that the Toshba and the Torah itself were one together and both had been given to the Children of Israel at Mt. Sinai. This school of though was very popular among the 'regular' people. In many ways this branch of Judaism was the basis for Rabbnic Judaism.

The main rivals of the Pharosees were the Saducees who rejected the Toshba and the Resurrection of the Dead. They were especially popular among the Aristocracy and the Clerics. Note that the Saducees are in many ways proto-Karaites.

The last major group were the Essenes but I don't know about their theology to comment about that.

The Karaites are a later splinter (literally Literalists in Hebrew) who as the name suggests follow Halacha based on the written word and it alone, disregarding Toshba(Oral Torah) and all it entails. This movement dates back to somewhen between the 7th and 9th centuey CE, and they used to be a significant portion of Judaism in the Middle Ages (40% of Jews at one point). The Khazar ruling elite presumably converted to this branch of Judaism but I'm not fully confident about that. They used to contest Rabannic Judaism and debates about theology between the two branches was common, in this context I'd like to mentiong RSG (Rabbi Saadia Gaon) who spearheaded the Rabbinic Judaism theological, intellectual fight against them. He also did a lot of other interesting stuff but it's a story for another day.

Even today Judaism is somewhat split with Orthodox Jews being completely dominant in Israel with Reformed and Conservative being a very insignificant minority, that's also the reason Israel's Jewish institutions (the Rabbanut mainly) are dominated by the Orthodox, while Reformed and Conservative Judaism are the prominent denominations among American Jews.

Orthodox Judaism main belief is the same of its predecessor (the Pharisees) that the Toshba and the Torah were given together to Moses at Mt. Sinai. The difference between this branch and the other modern ones stems from its full commitment to the Halacha. Within this branch there are various factions and also a cultural-geographic minor division, between the Sephardi community and the Ashkenazis. The main factions are the Haredim (popularly called ultra-orthodox for their uncompromising attitude to Halacha and resistance to modernization or reformation of Judaism), the Dati Leumi (Religious-National), the less strict Traditionalists and of course the secular Jews who are the majority 'Hilonim' . The Haredim have three main sub-groups: the Lithuanian school, the Hasidic school and the Sephardi school.