Without the world wars, mass production loses a powerful stimulus

How would the world differ if the world wars never happened?

Another major conflict remains likely, while some changes in mass manufacturing, including large-scale penicillin production, would probably take longer.

Removing the historical world wars leaves too many changes in diplomacy and technology to support a confident account of the whole century. Even following roughly the first twenty years would require numerous assumptions, and rivalry between the powers still makes another major war likely. The clearest suggested change is slower development of mass manufacturing across some industries. Penicillin provides the example: wartime demand helped turn a small-scale product into something manufactured in large quantities. Economic incentives could eventually produce the same expansion, but without the wartime pressure it would probably take longer.