The POD is in the early 13th century, and is essentially that the Habsburgs never extend their authority successfully over anything other than the eponymous Habsburg Castle. The POD was originally just to justify a one-off map I made of an independent Carniola, where I went back and tried to find the likeliest means to guarantee that. I put in enough work that the timeline's acquired a life of its own. By the present date, which is the 1860s, a lot of differences from OTL have started to mount up. One of the biggest ones is that, whilst some overseas possessions were taken, full blown colonialism as practised IOTL never fully becomes established, and so a lot of European states that IOTL are beefed up by their colonial possessions are not here. Another is that Bohemia retained its control over the HRE, but as a result of religious schism over Hussites, the HRE essentially split in the early 16th century. Lacking any kind of counterweight among the Catholic HRE states to Bohemia, they turned to France. So for some time, there's basically been a French HREmperor and a Bohemian HREmperor (which was itself a compromise to end really vicious religious wars), with this quasi-concensus breaking down early in the 19th century due to the emergence of radical political ideologies. The 'Orussian' state is actually a Mongol-Russian state. ITTL the Golden Horde converted to Orthodox Christianity rather than Islam, and whilst they still eventually collapsed, formed the basis for the Orussian state, with its capital at Smolensk, the spiritual heart of Mongolian Christianity, and whose King continues to claim Chinggisid heritage (and maintains a title of the Most Christian Khan). There's a lot of other Things that have mounted up over 600 years or so but that's a summary of a lot of the largest changes.
One other piece of context is that these Bohemian borders, for instance, are relatively recent, only really being current from 1848-1866 (with the latter being the present date of the setting). There's been some regions nicked from nearby states as a result of the '48 war, and also a large number of previously autonomous Hussite HRE states who have been integrated into a centralised Empire, some more willingly than others.