For 1st & 2nd grade, I taught both and it was fine. I did World on Mon and US on Thurs. For world, we read a ch. in Child’s History of the World, narrated, made a wall timeline card. For US, we read a ch. in American History Stories by Mara Pratt, narrated, completed a drawing and copywork sentence and put in our America folder. We had no confusion between the periods.
For 3rd grade, I’m switching to the SCM framework w/ more integrated Biblical history and a bit slower pace, but I am still continuing w/ the American History Story series, only as readers (actually audiobooks) w/ copywork, but no narrration.
Christie