You're right it's an emergent system, the seeds of it grew out of the systems before until it became the status quo. We didn't create or invent it deliberately, but it is comprised entirely of human behavior so in that sense we do actively recreate it. It's natural in the sense that literally everything is "natural", because it emerged organically. But to say it's " just the way things are" is a myopic and ahistorical viewpoint. Capitalism isn't trade itself, it's a protocol for conducting trade defined by how we as a species define and enforce property rights. Like all other systems there was a time before it and there will be a time after it.