Sorry, but I have to disagree. WW1 was rather one of the many causes that made social-security not working after WW2. The other big one being, well, WW2.
However, changing the financial scheme of social security away from a capital-backed one towards a "generational accounting" one IS what makes it not working today (unless the working population keeps it's proportional size in relation to the retirees).
However, changing the financial scheme of social security away from a capital-backed one towards a "generational accounting" one IS what makes it not working today (unless the working population keeps it's proportional size in relation to the retirees).