The French Revolution was caused, primarily, by a confluence of three factors:
The Russian Revolution was primarily caused by WWI:
I don’t know if the Russian legal system was as crusty as the French one, but the whole thing was run by Nicholas, which is not a good sign.
In both cases, the immediate priority for the revolutionary gov’t ought to be halting the deaths of the peasants. Things like standardizing weights and measures or executing the monarch, whether you like those ideas or not, far fall, fall below “getting people bread” and “getting rid of the machine guns.”
Unfortunately, at least in the Russian case, instead of replacing their old, peasant-starving gov’t with a gov’t sensitive to the caloric needs of its people, they replaced it with a gov’t that was massively better at not getting overthrown by starving peasants.
Leading promptly to the starvation of millions of people.