“I must have been asleep at Mass for about 40 years. When did the Catholic Church begin teaching that governments are supposed to be our brothers keeper?”
I think you’ve been asleep much longer than 40 years. Pope Leo XIII wrote: “And it is for this reason that wage-earners, since they mostly belong in the mass of the needy, should be specially cared for and protected by the government.” RERUM NOVARUM, 1891.
Leo XIII also wrote:
[I]n the case of the worker, there are many things which the power of the State should protect; and, first of all, the goods of his soul. For however good and desirable mortal life be, yet it is not the ultimate goal for which we are born, but a road only and a means for perfecting, through knowledge of truth and love of good, the life of the soul .
Personally I would say it began in the first century AD. If you’re looking for documentation you can find sources that definitely talk about it in the Middle Ages.
It says protect not run or mandate