York which used to be England’s capital but then they later came second in a scrap with Lancaster.
I seem to recall this all gets rather murky, with the Yorkists actually being mainly from Lancashire*, the house of Lancaster mostly being from (when not being foreign) and drawing support from Yorkshire*, the Yorkists defeating the lancasters and wiping out the male line then a distant lancastrian (tudor) cousin invades from France, kills York, marries his sister and puts an end to the whole thing.
*obviously this isn’t actually true, but in a very familiar twist they were all friends of the government of the day, parachuted into profitable and trouble free fiefdoms outside of London who had no idea where their particular barony was. So they sided with whomever they expected to win/pay better/treat them worst if they picked wrong, regardless of the reality of their little bit of the world being only 100 yards from York or Lancaster. They occasionally headed north to campaign and fight the opposition a bit to make sure they were on the list for the good jobs but in blatant disregard for the benefit or otherwise of their subjects.