Loads of women in the workforce in WWII. Was there anything like HR? (Not counting the recruiting departments, which were focused on finding & retaining workers in a very tight labor market.)

Instead of "women in the workforce", I'd say it was changing society and social norms. A century-ish ago, in quite a few sorts of places, workspace disputes might well be settled with fists. (Yes, there were many norms and unwritten rules about that.) Post-WWII, there was a long trend of gentrifying social mores, which discouraged such things. New laws and legal norms encouraged lawsuits over things previously tolerated, or settled informally. And more than just women, civil rights laws and norms pushed into the workplace. Bring in the lawyers, reporters, new public ideals - and a business really needed an HR Dept., to prevent disasters.

(Yes, this pretty is US-specific.)