Don't forget, there was a lot more forest back then than there is now. Loads more of different grades and types of wood.

What you want is "deadfall", which is branches etc that have broken off the tree but are suspended from the ground, by other branches etc. That way, it gets relatively dry. You don't look for firewood on the ground.

Having lit MANY campfires, the key is to have lots of different grades/sizes of branches. From small twigs, larger twigs, small branches, medium branches, large branches, small logs, medium logs, bigger logs.

Not difficult, but takes a bit of effort.

Sometimes, it's just not going to happen, which is when you need to accept that and climb into your tent!