You're a young male off to fight in either of the most brutal wars in history. This might just be the last time you see your wife, so you have nothing to lose in having a child at that point, as you have a much higher chance of never being able to do so later when things are better.

Alternatively you lived in a city reduced to ruins by the war, everything you knew or had is gone and you have no idea when or even if you'll be able to recover. Having a child doesn't involve as much of a concern over whether or not you can give them a better upbringing because things couldn't really get much worse in the first place.

Now, on the other hand, if you're talking about post-war, the world was recovering, there were opportunities everywhere, the future was looking more hopeful. You could just have kids and trust that they'd live a more comfortable life than yourself.

Nowadays, we're at this awkward point where there's just enough uncertainty and instability in the future, yet not bad enough that people have nothing to lose that people would rather wait or just not have any kids at all.

Yeah I mean it makes sense as a story. But it also makes sense not to have a kid if you think you’re going to die at war. Both stories are perfectly believable, I’d say. And likewise it also makes sense not to bring a child into a bombed out hellhole with severely limited food rations.

And in the 50s the future was looking good in some ways, but people also lived under a visceral fear of nuclear annihilation. These are all just feelings people may or may not have.

Ultimately, I think it’s much more complicated than saying that circumstances in the past made it easier for people to decide to have children.