1. Bad harvests=> to starving peasants. Starving peasants will risk death for food.
2. The gov’t went deep into debt to fund expensive wars and could extract no more taxes from the starving peasants.
3. The legal system was crusty and inefficient, due to old age.

The Russian Revolution was primarily caused by WWI:

1. It was far more expensive than Russia could afford,
2. Unarmed peasants ordered to fling themselves in front of German machine guns react a lot like starving peasants told to go eat cake
3. Probably a lot of starving peasants.

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.