>the journey to modern democracies involved centuries of concessions by kings to the emerging middle classes
Eh, sort of disagree. The journey to modern democracy started with centuries of concessions by kings, first to other nobles (Magna Carta, etc.) Then, to other local power brokers like large landowners, business elites, etc. None of these parties wanted one single figure to have absolute power over their affairs & finances, mostly because they tended to make terrible decisions (random wars, taxation, and so on). Early proto-parliamentary systems in the UK, Netherlands, Scandinavia, Japan in the 19th century etc. were just a council of local, powerful elites who wanted to check the power of the king. The 'middle class' part came absolutely last
I live in the UK, so for me, 'middle class' means those large landowners and business elites who aren't part of the nobility.
The US is very generous with its use of the labels of privilege.