In the early 1880s, Chancellor Otto Von Bismarck of Germany had a problem. Marxist unrest was spreading across Europe and some of his own countrymen were calling for socialist reforms. To take the wind out of their sails and stave off more radical policies, Bismarck concocted a first-of-its-kind social insurance program wherein the national government would contribute to the pensions of nonworking older Germans.

Along with German Emperor William the First, Bismarck announced the idea in 1881, and the pair made their case to the Reichstag, or German Parliament, that  “those who are disabled from work by age and invalidity have a well-grounded claim to care from the state.”*

According to the historians at the American Social Security Administration, the usual explanation for that magic number of 65 is that, at the time the plan was created, that happened to be Bismarck’s own age. The story doesn’t hold up, though. Germany initially chose 70 as its retirement age, and didn’t lower it to 65 until long after Bismarck was dead. The choice for the age of eligibility was actually more of a shrewd, and maybe a little cynical, cost-saving measure: it closely matched the average German life expectancy at the time.

Even though his plan was to flank the Marxists, Bismarck (pictured) still drew criticism for the old-age pensions, and the far-right politician was labeled a socialist. The same charge was slapped on President Franklin Roosevelt when he imported the idea to the U.S. decades later. The Committee on Economic Security, which launched the American Social Security system in 1935, selected 65 as the retirement age, but the SSA says that federal government wasn’t simply following Germany’s lead. Their choice was, like the Germans’, pragmatic. Roughly half of the existing private and state-run old-age pension systems, as well as the federal Railroad Retirement System, were using 65 as their retirement age, and the other half were using 70. It was practical for the federal plan to sync up with one half or the other, and the government’s actuarial studies suggested that starting the pensions at age 65 would allow for a system that could easily be sustained with moderate payroll taxes.

That sustainability wouldn’t last, though. In the 1980s, the SSA saw that changes in the number of people in the workforce and in retirement would require reforms to the plan. Congress has since had to make the occasional adjustment to Social Security withholding taxes and the age of eligibility. Currently, the retirement age for full benefits depends on the year a person was born. Meanwhile, the Germans have had to make adjustments to their own historic system, proposing a gradual increase of the official retirement age to 67 over the next few years.

* Just a few years later, Bismarck and William also passed an Imperial insurance order — known in German as the Reichsversicherungsverordnung — which mandated certain workers to pay premiums to health insurance funds.