> China generally feels as though it was 'left out' of the modernization of politics that occurred in the mid-20th Century (and they have a point)
I'm not sure they have a point. They were not nearly as powerful of a country back then. Here's the GDPs of several countries from 1960 to 1980[0]. I also literally have to remove the US because adding it makes it impossible to differentiate the others. 1960-1962 they were also declining. I mean we would laugh at Canada if they made a complaint about being "left out" (read: were able to participate but no one really cared) because Canada has no leverage.
To make matters worse, the analogy is more akin to being upset that your rich neighbor is not taking your financial advice while you are standing in front of all your savings that you have lit on fire and are actively searching for more cash to add. See the Korean War (1950-1953), First Taiwan Strait Crisis (1954-1955), Hundred Flowers Campaign (1956-1957), Great Leap Forward (1958–1962), Great Chinese Famine (1959-1961), Sino-Soviet split (1961–1989), Cultural Revolution (1966-1976), Red August, and so on. China was not a stable country at the time. It sided against the interests of the most powerful groups at the time (choosing Communism over Capitalism/Democracy), and to make matters worse didn't even align itself with the other major power that was opposing "the West" (USSR). OF COURSE China was "left out." It would have been insane to "include" them just the same way it would be insane to "include" Liechtenstein. It is also insane to be upset about no one taking you seriously when you were a nobody, even if you now became a somebody. It's frustrating, I get it, but it is a silly notion to think that your status today warrants others taking you seriously in the past. Those are two different people just as those are two different Chinas.
[0] https://data.worldbank.org/indicator/NY.GDP.MKTP.CD?end=1981...