The original manuscript clearly has the definite article the rather than the determiner this. The e at the end of the ends in a slight flourish, which apparently led Oliver Cowdery to miscopy the the as this in the printer’s manuscript. Either reading actually works, so the correct decision should be to follow the earliest textual source, namely the (the reading in 𝓞). For other instances where the and this have been mixed up in the text, see under 2 Nephi 10:23.
Summary: Restore the definite article the before little force in Alma 56:17 (“the little force which I brought with me”).