When Marx was writing, it was common for historian's to try and formulate grand predictive theories explaining all of the past, the present and how the world would inevitably progress towards a better one.

The "hard times create hard men, hard men create good times, good times create soft men, soft men create hard times" idealist rubbish fascists love to spout was a popular cyclic view of history when Marx was writing as was "by nature human are evil, as culture, technology and civilisation progress humans inevitably become better people and closer to god" progressivist theories of history.

Since WWI, historians (including most marxist historians) have acknowledged that both sweeping predictive theories and talking about anything as "inevitable" isn't really realistic and instead tend to phrase major schools of thought as useful lenses by which to examine the past rather than a grand theory of history and predictions or causal mechanisms as "here's something that was a factor in this event happening" or "here's a mechanism by which this could happen".

So will, as Marx said, contradictions inherent in capitalism inevitably lead to the advent of communist and then socialist society?

Is class struggle the only factor influencing the course of history and the present?

Absolutely not, nothing's inevitable until it's happened, and class struggle, while a major factor in why things happen and an extremely useful lens to view current and historical events through, is far from the only factor influencing the course of things.

But viewing history and current events through a marxist materialist class struggle lens is often enlightening and extremely useful, especially to us as socialists. The contradictions Marx described do exist, and they (among other factors) can and have been exploited by motivated and united working class people to destroy capitalism and start building socialism.

Our victory is not inevitable, but it is possible and Marx's theories, if not a prophesy of the only path industrial society can possibly take, do highlight mechanisms of social change, ways capitalism is tearing itself apart, and a way of viewing society and our collective interests that are utterly invaluable to us as workers suffering under capitalism and trying to find a way to tear it down and build something better in its place.