I think I get it
This is my interpretation of Salad Fingers. He is a man living in an allied country (usa, canada, england most likely) during the period of WW1 (often referred as the Great War) He lived in a rural area and when WW1 started SF's little brother, possibly Jeremy Fisher and Hubert Cumberdale and Majory Steward Baxter and all of SF's friends left to fight for the allies in WW1, leaving SF all by himself. Overtime, SF has grown insane, waiting for his friends to return, keeping himself "busy" in his own world, just waiting for the war to end and his life to return to as it was.