What are we to disciple?
The object of “disciple” is “all nations” (panta ta ethnE), not “those of all nations” (hoi ek pantOn tOn ethnOn). So we are to disciple nations qua nations.
By the time we get to “baptising” the object is simply “them” (autous).
1. Nations are meant throughout. “Baptise England” means “Adopt England into the kingdom” – i.e. the command to baptise is figurative.
2. People in nations are meant throughout. We are intended to read the synecdoche of “baptising” back into “disciple”.
3. Nations are meant when it comes to “discipling” and “individuals in nations” are meant when it comes to baptising.
I think I favour the third option, or possibly the first. If Jesus had wanted to say we merely baptise people in nations, he could have said so with the Greek I used earlier. He didn’t. However when it comes to baptism, a synecdochic reading makes most sense, and he didn’t say “baptising those of them” to avoid being obscure.