> It makes perfect logical sense. The predictions changed behavior.

This is absolute nonsense. That's not what models are nor how they work. Marx makes it pretty clear that his theories are the definitive course of History, which obviously isn't the case.

> The Communist Manifesto itself includes a list of electoral demands for reforms, that includes things like e.g. free primary education. What it doesn't include is a call for revolution, but a reactive suggestion that if forced by circumstance the working class makes itself the ruling class by means of revolution, then that would in a stroke sweep away the bourgeois state.

What are you talking about? The Communist Manifest to explicitly calls for revolutions and radical fracture of societal values through the entire text. Incremental improvements were always used for making certain points about class struggle but was never proposed seriously as a solution.

> Marx left the door open for electoral politics already then. Indeed, the Communist Manifesto also expresses his support for the activity of the Chartists in the UK, who aimed to expand suffrage, to the consternation of more hardline revolutionaries who saw it as pointless.

They merely talk about Chartists if not for a mere moral support and used as an example that History always leads to class struggles and never as an alternative to the revolution.

> Later, one of Marx own most famous works - Critique of the Gotha Programme - does not critique said program by rejecting the idea of electoral policies, but instead critiques and suggests changes to said electoral program set forth by the Social Democratic Workers Party in Germany, a party closely aligned with Marx and Engels, and one of forerunners of the SPD. And incidentally one of the parties that helped scare Bismark into action.
The founder of social democracy - Eduard Bernstein - was a personal friend of Marx, and a Marxist himself. Modern social democracy is a very different thing, but from the start it was strongly aligned to communism, with many modern social democratic parties tracing their origin to Marxist organisations.
Incidentally, the Erfurt Programme of the SPD, published in 1891, was written by Kautsky, Bebel and Bernstein, all three of whom were outspoken Marxists, though Kautsky and Bebel were much more "orthodox" in their support for the need for revolution.
The sharp separation between social-democrats and revolutionary socialists of various shades first started taking shape towards the very end of the century and sped up with a number of social-democratic parties supporting World War I, leading to splits, and further splits after the Bolshevik coup. That separation was not "complete" until the late 1920's with the Stalinisation of Komintern.

An idea does carry over all the baggage of their progenitors. X was friend with Y, ok, so what? That's high school gangs politics at this point.

> Marx didn't predict that a capitalist economy would immediately collapse if it did not have access to new geographic markets, so this is entirely flawed logic. His prediction is very simple:
Companies will eventually need to reduce the cost of labour per unit of value produced to survive, because it will be the easiest remaining way to compete, and this will eventually drive unemployment, and that this will eventually lead to escalating crises.
But a pre-requisite is that labour first needs to become the easiest factor to optimise.

There are various signs before collapses. Collapses have a series of events and aggravating context that make them possible. What Marx based his predictions on are just not really there or at least at a scale that makes them possible. Remunerations continued to increase and worker productivity has also increased. And no, labor is not always to optimize when technology is taken into account.

> There's nothing in Marx' predictions that goes against this. This goes back to the insistence that capitalism is first at threat of crises once reducing the cost of labour becomes the primary competitive lever.
I pointed to China, India and Africa explicitly because they still see the easy gains of developing economies, where there are a plethora of ways to drive growth that are easy enough that focusing on reducing total labour costs are not worthwhile. Just like Europe and the US exported low-paid work to India and China, China and India are exporting low paid work to Bangladesh, Vietnam and Africa, and in doing so allowing for salary growth in their own countries. But even within Africa this is happening between countries at different levels of development.
The point I was making is explicitly that we have no way of determining whether or not Marx was right about what happens when there are no further places to export competitive pressure until those places have exhausted the easy gains.
Basically: Once even sub-Saharan Africa starts seeing GDP growth rates closely track declining population growth numbers is the first point in time when we will actually be able to start making a judgement about whether his prediction that aggregate labour costs will be driven down is true or not, and whether or not that will have the effect of causes crises
Were at a minimum many decades away from that, maybe much longer.
And he may well be wrong, but we can't tell anytime soon.

Again, as new markets fail to appear with the world's there is no real tendencies for that to happen. And also basing the deconstruction and reconstruction of society over an hypothesis is just not prone to good outcomes to say the least.