The end of S5 was a total cliffhanger. I didn't expect Steven Knight to rewrite history to suit his story like Quentin Tarantino does. Poor Tommy Shelby is left totally discombobulated, hoodwinked by a greater power.
This is the story of the Shelby family in the inter war years of 1919 to 1939. The finale covers the years from 1934 to 1939. We learn that Charlie Solomons, Alfie's uncle has been wacked by the Boston Irish outfit. I'm not sure if it has any bearing on the story, this was also the time that the NYC Jewish and Italian outfits banded together to form Murder Inc.