The cycles you mention are each very interesting.

Flash/Silverlight/HTML5/WASM - this, to me, is a story of a technology being useful, then growing to give too much power to web publishers - who tend to abuse any given power - then reverting to a weaker technology in order to unscrew the web. Rinse, repeat - HTML5 is already rapidly approaching peak Flash, and introduction of WASM isn't going to help here.

Soap/REST/JSON API - you could call it a story of simplification, but I don't get how it even came to be. That is, how XML gained so much popularity, given that simpler and better tools for almost all of its uses were already available and known.

I still don’t understand what problems people have with xml. The json vs xml debate very much feels like the tab vs white space debate to me.

I suspect the reasons that XML ultimately lost are:

1. You could represent it as a nested structure of your language's standard lists & maps, which you already know the API of, which you could directly operate on. For dynamic languages, this is much faster to stick a prototype together, even if it bites you in the ass eventually. But by the stage, you've already chosen JSON.

2. It was less characters to manually type.

3. Particular uses of XML were extremely verbose. The S in SOAP stood for Simple, which looks ironic in retrospect.

4. In a time when payloads didn't routinely use compression, the closing tags could be a noticeable increase in size.

5. The vast majority of communication that now uses JSON didn't benefit significantly from XPath (people prefer to navigate data structures using their language features, not a generic API), namespaces, DTDs, XML Schema etc.

In about that order.

You could argue that much of this is superficial, and it is, but the industry has shown time and again that lowering the barrier to entry, even in ways that make little difference in the long run, usually wins out.

The sad thing about #5 is that XPath is epic and trying to simulate queries using it in almost any programming language without just implementing it is tons of grunt work :(. When I a trying to parse through some complex data structure I still to this day find myself getting tired after writing a bunch of nested for loops resulting in my saying "screw this", convering the data to XML, and making short work of the problem with XPath (which only got better and better in subsequent releases of XSL/T).

You forgot my favorite one:

6. Too easy to accidentally reinvent Lisp via xml.

I thought it was funny the first time I ran into an instance of it happening, which quickly turned into horror. Not only was the logic split, but it meant mentally parsing this:

  <If><RegEx string="{AZ*}"><Register /></RegEx></If>

I mean, it sort of makes sense...?

not that JSON is immune to this - mongodb's query interface is a reinvention of the same, but in JSON.

Basically it's a Markup Language, not a data transfer language, so it was far from ideal to use it as one. See for example the ambiguity between what should go into tag attributes vs. tag content etc. Also the eXtensibility makes things too complicated for many use-cases. You don't have to care about any of this with JSON.

XML started out simple, and then caught really nasty FeatureCreep and DesignByCommittee.

Extreme bloat of the format, which makes it in practice both wasteful and not human-readable.

For me it's about simplicity. Xml is more featureful, more difficult to write a processor for, and more difficult to write out and read by hand.

The X in AJAX is indeed XML. Quickly appeared though that XML is too heavyweight and redundant for the browser (XML DOM!) and even for the internet speeds at that time, while JSON is as simple as JS' object literal. Web 2.0 adapting JSON formed a critical mass so that later (almost) everyone and everything went (almost) full JSON.

> redundant for the browser (XML DOM!)

I don't quite get this part.

Both HTML & XML cater for DOM models. I think this is & was appropriate.

Browsers had support for executing XSL stylesheets because it made sense for a lot of use cases.

JSON is easier to use from Javascript

Json is less verbose than XML, easier to read.