Incidentally I remember my history teacher commenting that even if Marx didn't exist at that time, communism would still be born around that time in history.
Marx himself would say so. Key to Marxism is studying history to come up with a scientific theory which predicts the future course of society. If individuals can change the course of history through shear force of their will, bending society in unpredictable ways to suit their individual fancy, that throws a wrench into it.
But can anybody seriously say that if not for Napoleon, there surely would have been some other French general, inspired by Julius Caesar to conquer everything he could, who was simultaneously also a master tactician with enough skill to get as far as Napoleon did? I can buy the premise that somebody else in that political environment might have tried, but to get so far and embroil most of the world in war as Napoleon did wasn't a deterministic predictable consequence of the circumstance. You can probably predict a civil war, but not the Napoleonic Wars.
There's definitely problems with a 100% structuralist view of history too make no mistake. Things like politics, battles and wars are more prone to the effects of outliers and random chance just by their nature, you can't have 1000 people try to conquer Italy with one of the least loved chunks of the French Army at the same time, unlike how you can have 1000 people working on radio or flight at a time. On the other side of the coin without the French Revolution which he had no part in creating or driving he would have likely stayed a minor artillery officer or less in the Acien regime.
