They also didn’t intentionally starve the populace, that was a byproduct of pissing off the world.

Given they destroyed ship delivering food to the UK. Knowing the UK imported something like 50+% of all food at the time.

The UK also did much the same. Bombing rail etc.

Starving the population was an intentional side effect of trying to limit resources getting to an enemy.

So the honest answer is things were less efficient.

But starvation has been a common practice since rome. Salting the fieilds etc. And likely before then.

Honestly the Geneva convention was the first time anyone expected otherwise.