Regulus would be careful around Severus until he was sure he didn't have to be. Friends they might have been at one point, what did that mean if the older man he was looking at was still a dyed-in-the-wool believer?
And Regulus did not have his wand.
The last thing he wanted was to be caught on the end of a devout Death Eater's wand.
"You'd be mistaken," Regulus said, "The Americans are particularly hung up on wars and this one in particular. It seems to be a culture-defining moment." Hence why he'd picked up a book analyzing the ideology of this particular period.
"Is that what you're here for? Literature recommendations?"