I've had great fun tracking descendents of my Hogans and Careys who, in the 1880's, swapped the mines and shipyards of Northumberland for the mines of Pennsylvania and the shipyards of Ohio.
1940 census was especially interesting - quite a lot of people aged 15 to 25 and people 55 and over who didn't have any occupation recorded.
It was only when I came across one household with two residents recorded as employed in "new work" that the penny dropped, as it were. 1930's - the Great Depression, Roosevelt's New Deal, job creation schemes.
It made me think about my poor old Dad living in the North-East and leaving school in 1920 but never managing to procure a permanent job until he was called up the day WW2 began in 1939.
He was just one of thousands in that situation. But unlike the USA, there was no comparable UK census to show us just how widespread unemployment was and how there were whole families with not one single adult earning a wage.

Jay